diff --git a/resources/sql/autopatches/20200417.viewstate.01.storage.sql b/resources/sql/autopatches/20200417.viewstate.01.storage.sql
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20200417.viewstate.01.storage.sql
@@ -0,0 +1,9 @@
+CREATE TABLE {$NAMESPACE}_differential.differential_viewstate (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  viewerPHID VARBINARY(64) NOT NULL,
+  objectPHID VARBINARY(64) NOT NULL,
+  viewState LONGTEXT NOT NULL COLLATE {$COLLATE_TEXT},
+  dateCreated INT UNSIGNED NOT NULL,
+  dateModified INT UNSIGNED NOT NULL,
+  UNIQUE KEY `key_viewer` (viewerPHID, objectPHID)
+) ENGINE=InnoDB, COLLATE {$COLLATE_TEXT};
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -713,6 +713,8 @@
     'DifferentialUnitStatus' => 'applications/differential/constants/DifferentialUnitStatus.php',
     'DifferentialUnitTestResult' => 'applications/differential/constants/DifferentialUnitTestResult.php',
     'DifferentialUpdateRevisionConduitAPIMethod' => 'applications/differential/conduit/DifferentialUpdateRevisionConduitAPIMethod.php',
+    'DifferentialViewState' => 'applications/differential/storage/DifferentialViewState.php',
+    'DifferentialViewStateQuery' => 'applications/differential/query/DifferentialViewStateQuery.php',
     'DiffusionAuditorDatasource' => 'applications/diffusion/typeahead/DiffusionAuditorDatasource.php',
     'DiffusionAuditorFunctionDatasource' => 'applications/diffusion/typeahead/DiffusionAuditorFunctionDatasource.php',
     'DiffusionAuditorsAddAuditorsHeraldAction' => 'applications/diffusion/herald/DiffusionAuditorsAddAuditorsHeraldAction.php',
@@ -2735,6 +2737,8 @@
     'PhabricatorChangePasswordUserLogType' => 'applications/people/userlog/PhabricatorChangePasswordUserLogType.php',
     'PhabricatorChangesetCachePurger' => 'applications/cache/purger/PhabricatorChangesetCachePurger.php',
     'PhabricatorChangesetResponse' => 'infrastructure/diff/PhabricatorChangesetResponse.php',
+    'PhabricatorChangesetViewState' => 'infrastructure/diff/viewstate/PhabricatorChangesetViewState.php',
+    'PhabricatorChangesetViewStateEngine' => 'infrastructure/diff/viewstate/PhabricatorChangesetViewStateEngine.php',
     'PhabricatorChartAxis' => 'applications/fact/chart/PhabricatorChartAxis.php',
     'PhabricatorChartDataQuery' => 'applications/fact/chart/PhabricatorChartDataQuery.php',
     'PhabricatorChartDataset' => 'applications/fact/chart/PhabricatorChartDataset.php',
@@ -6783,6 +6787,11 @@
     'DifferentialUnitStatus' => 'Phobject',
     'DifferentialUnitTestResult' => 'Phobject',
     'DifferentialUpdateRevisionConduitAPIMethod' => 'DifferentialConduitAPIMethod',
+    'DifferentialViewState' => array(
+      'DifferentialDAO',
+      'PhabricatorPolicyInterface',
+    ),
+    'DifferentialViewStateQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'DiffusionAuditorDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'DiffusionAuditorFunctionDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'DiffusionAuditorsAddAuditorsHeraldAction' => 'DiffusionAuditorsHeraldAction',
@@ -9130,6 +9139,8 @@
     'PhabricatorChangePasswordUserLogType' => 'PhabricatorUserLogType',
     'PhabricatorChangesetCachePurger' => 'PhabricatorCachePurger',
     'PhabricatorChangesetResponse' => 'AphrontProxyResponse',
+    'PhabricatorChangesetViewState' => 'Phobject',
+    'PhabricatorChangesetViewStateEngine' => 'Phobject',
     'PhabricatorChartAxis' => 'Phobject',
     'PhabricatorChartDataQuery' => 'Phobject',
     'PhabricatorChartDataset' => 'Phobject',
diff --git a/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php b/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
--- a/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
+++ b/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
@@ -89,13 +89,16 @@
     $engine = new PhabricatorMarkupEngine();
     $engine->setViewer(new PhabricatorUser());
 
+    $viewstate = new PhabricatorChangesetViewState();
+
     $parsers = array();
     foreach ($changesets as $changeset) {
-      $cparser = new DifferentialChangesetParser();
-      $cparser->setUser(new PhabricatorUser());
-      $cparser->setDisableCache(true);
-      $cparser->setChangeset($changeset);
-      $cparser->setMarkupEngine($engine);
+      $cparser = id(new DifferentialChangesetParser())
+        ->setViewer(new PhabricatorUser())
+        ->setDisableCache(true)
+        ->setChangeset($changeset)
+        ->setMarkupEngine($engine)
+        ->setViewState($viewstate);
 
       if ($type == 'one') {
         $cparser->setRenderer(new DifferentialChangesetOneUpTestRenderer());
diff --git a/src/applications/differential/controller/DifferentialChangesetViewController.php b/src/applications/differential/controller/DifferentialChangesetViewController.php
--- a/src/applications/differential/controller/DifferentialChangesetViewController.php
+++ b/src/applications/differential/controller/DifferentialChangesetViewController.php
@@ -165,21 +165,6 @@
     list($range_s, $range_e, $mask) =
       DifferentialChangesetParser::parseRangeSpecification($spec);
 
-    $parser = id(new DifferentialChangesetParser())
-      ->setViewer($viewer)
-      ->setCoverage($coverage)
-      ->setChangeset($changeset)
-      ->setRenderingReference($rendering_reference)
-      ->setRenderCacheKey($render_cache_key)
-      ->setRightSideCommentMapping($right_source, $right_new)
-      ->setLeftSideCommentMapping($left_source, $left_new);
-
-    $parser->readParametersFromRequest($request);
-
-    if ($left && $right) {
-      $parser->setOriginals($left, $right);
-    }
-
     $diff = $changeset->getDiff();
     $revision_id = $diff->getRevisionID();
 
@@ -197,6 +182,35 @@
       }
     }
 
+    if ($revision) {
+      $container_phid = $revision->getPHID();
+    } else {
+      $container_phid = $diff->getPHID();
+    }
+
+    $viewstate_engine = id(new PhabricatorChangesetViewStateEngine())
+      ->setViewer($viewer)
+      ->setObjectPHID($container_phid)
+      ->setChangeset($changeset);
+
+    $viewstate = $viewstate_engine->newViewStateFromRequest($request);
+
+    $parser = id(new DifferentialChangesetParser())
+      ->setViewer($viewer)
+      ->setViewState($viewstate)
+      ->setCoverage($coverage)
+      ->setChangeset($changeset)
+      ->setRenderingReference($rendering_reference)
+      ->setRenderCacheKey($render_cache_key)
+      ->setRightSideCommentMapping($right_source, $right_new)
+      ->setLeftSideCommentMapping($left_source, $left_new);
+
+    $parser->readParametersFromRequest($request);
+
+    if ($left && $right) {
+      $parser->setOriginals($left, $right);
+    }
+
     // Load both left-side and right-side inline comments.
     if ($revision) {
       $query = id(new DifferentialInlineCommentQuery())
@@ -249,7 +263,7 @@
     $engine->process();
 
     $parser
-      ->setUser($viewer)
+      ->setViewer($viewer)
       ->setMarkupEngine($engine)
       ->setShowEditAndReplyLinks(true)
       ->setCanMarkDone($can_mark)
diff --git a/src/applications/differential/parser/DifferentialChangesetParser.php b/src/applications/differential/parser/DifferentialChangesetParser.php
--- a/src/applications/differential/parser/DifferentialChangesetParser.php
+++ b/src/applications/differential/parser/DifferentialChangesetParser.php
@@ -45,7 +45,6 @@
   private $disableCache;
   private $renderer;
   private $characterEncoding;
-  private $highlightAs;
   private $highlightingDisabled;
   private $showEditAndReplyLinks = true;
   private $canMarkDone;
@@ -61,6 +60,8 @@
   private $viewer;
   private $documentEngineKey;
 
+  private $viewState;
+
   public function setRange($start, $end) {
     $this->rangeStart = $start;
     $this->rangeEnd = $end;
@@ -85,13 +86,13 @@
     return $this->showEditAndReplyLinks;
   }
 
-  public function setHighlightAs($highlight_as) {
-    $this->highlightAs = $highlight_as;
+  public function setViewState(PhabricatorChangesetViewState $view_state) {
+    $this->viewState = $view_state;
     return $this;
   }
 
-  public function getHighlightAs() {
-    return $this->highlightAs;
+  public function getViewState() {
+    return $this->viewState;
   }
 
   public function setCharacterEncoding($character_encoding) {
@@ -183,7 +184,6 @@
 
   public function readParametersFromRequest(AphrontRequest $request) {
     $this->setCharacterEncoding($request->getStr('encoding'));
-    $this->setHighlightAs($request->getStr('highlight'));
     $this->setDocumentEngineKey($request->getStr('engine'));
 
     $renderer = null;
@@ -378,15 +378,6 @@
     return $this;
   }
 
-  public function setUser(PhabricatorUser $user) {
-    $this->user = $user;
-    return $this;
-  }
-
-  public function getUser() {
-    return $this->user;
-  }
-
   public function setCoverage($coverage) {
     $this->coverage = $coverage;
     return $this;
@@ -604,7 +595,7 @@
   }
 
   private function getHighlightFuture($corpus) {
-    $language = $this->highlightAs;
+    $language = $this->getViewState()->getHighlightLanguage();
 
     if (!$language) {
       $language = $this->highlightEngine->getLanguageFromFilename(
@@ -634,6 +625,8 @@
   }
 
   private function tryCacheStuff() {
+    $viewstate = $this->getViewState();
+
     $skip_cache = false;
 
     if ($this->disableCache) {
@@ -644,7 +637,8 @@
       $skip_cache = true;
     }
 
-    if ($this->highlightAs) {
+    $highlight_language = $viewstate->getHighlightLanguage();
+    if ($highlight_language !== null) {
       $skip_cache = true;
     }
 
@@ -844,7 +838,7 @@
       count($this->new));
 
     $renderer = $this->getRenderer()
-      ->setUser($this->getUser())
+      ->setUser($this->getViewer())
       ->setChangeset($this->changeset)
       ->setRenderPropertyChangeHeader($render_pch)
       ->setIsTopLevel($this->isTopLevel)
diff --git a/src/applications/differential/query/DifferentialViewStateQuery.php b/src/applications/differential/query/DifferentialViewStateQuery.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/query/DifferentialViewStateQuery.php
@@ -0,0 +1,64 @@
+<?php
+
+final class DifferentialViewStateQuery
+  extends PhabricatorCursorPagedPolicyAwareQuery {
+
+  private $ids;
+  private $viewerPHIDs;
+  private $objectPHIDs;
+
+  public function withIDs(array $ids) {
+    $this->ids = $ids;
+    return $this;
+  }
+
+  public function withViewerPHIDs(array $phids) {
+    $this->viewerPHIDs = $phids;
+    return $this;
+  }
+
+  public function withObjectPHIDs(array $phids) {
+    $this->objectPHIDs = $phids;
+    return $this;
+  }
+
+  public function newResultObject() {
+    return new DifferentialViewState();
+  }
+
+  protected function loadPage() {
+    return $this->loadStandardPage($this->newResultObject());
+  }
+
+  protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
+    $where = parent::buildWhereClauseParts($conn);
+
+    if ($this->ids !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'id IN (%Ld)',
+        $this->ids);
+    }
+
+    if ($this->viewerPHIDs !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'viewerPHID IN (%Ls)',
+        $this->viewerPHIDs);
+    }
+
+    if ($this->objectPHIDs !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'objectPHID IN (%Ls)',
+        $this->objectPHIDs);
+    }
+
+    return $where;
+  }
+
+  public function getQueryApplicationClass() {
+    return 'PhabricatorDifferentialApplication';
+  }
+
+}
diff --git a/src/applications/differential/storage/DifferentialDiff.php b/src/applications/differential/storage/DifferentialDiff.php
--- a/src/applications/differential/storage/DifferentialDiff.php
+++ b/src/applications/differential/storage/DifferentialDiff.php
@@ -716,6 +716,8 @@
   public function destroyObjectPermanently(
     PhabricatorDestructionEngine $engine) {
 
+    $viewer = $engine->getViewer();
+
     $this->openTransaction();
       $this->delete();
 
@@ -730,6 +732,13 @@
         $prop->delete();
       }
 
+      $viewstates = id(new DifferentialViewStateQuery())
+        ->setViewer($viewer)
+        ->withObjectPHIDs(array($this->getPHID()));
+      foreach ($viewstates as $viewstate) {
+        $viewstate->delete();
+      }
+
     $this->saveTransaction();
   }
 
diff --git a/src/applications/differential/storage/DifferentialRevision.php b/src/applications/differential/storage/DifferentialRevision.php
--- a/src/applications/differential/storage/DifferentialRevision.php
+++ b/src/applications/differential/storage/DifferentialRevision.php
@@ -1002,9 +1002,11 @@
   public function destroyObjectPermanently(
     PhabricatorDestructionEngine $engine) {
 
+    $viewer = $engine->getViewer();
+
     $this->openTransaction();
       $diffs = id(new DifferentialDiffQuery())
-        ->setViewer($engine->getViewer())
+        ->setViewer($viewer)
         ->withRevisionIDs(array($this->getID()))
         ->execute();
       foreach ($diffs as $diff) {
@@ -1022,6 +1024,13 @@
         $dummy_path->getTableName(),
         $this->getID());
 
+      $viewstates = id(new DifferentialViewStateQuery())
+        ->setViewer($viewer)
+        ->withObjectPHIDs(array($this->getPHID()));
+      foreach ($viewstates as $viewstate) {
+        $viewstate->delete();
+      }
+
       $this->delete();
     $this->saveTransaction();
   }
diff --git a/src/applications/differential/storage/DifferentialViewState.php b/src/applications/differential/storage/DifferentialViewState.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/storage/DifferentialViewState.php
@@ -0,0 +1,132 @@
+<?php
+
+final class DifferentialViewState
+  extends DifferentialDAO
+  implements PhabricatorPolicyInterface {
+
+  protected $viewerPHID;
+  protected $objectPHID;
+  protected $viewState = array();
+
+  private $hasModifications;
+
+  protected function getConfiguration() {
+    return array(
+      self::CONFIG_SERIALIZATION => array(
+        'viewState' => self::SERIALIZATION_JSON,
+      ),
+      self::CONFIG_KEY_SCHEMA => array(
+        'key_viewer' => array(
+          'columns' => array('viewerPHID', 'objectPHID'),
+          'unique' => true,
+        ),
+        'key_object' => array(
+          'columns' => array('objectPHID'),
+        ),
+      ),
+    ) + parent::getConfiguration();
+  }
+
+  public function setChangesetProperty(
+    DifferentialChangeset $changeset,
+    $key,
+    $value) {
+
+    if ($this->getChangesetProperty($changeset, $key) === $value) {
+      return;
+    }
+
+    $properties = array(
+      'value' => $value,
+      'epoch' => PhabricatorTime::getNow(),
+    );
+
+    $diff_id = $changeset->getDiffID();
+    if ($diff_id !== null) {
+      $properties['diffID'] = (int)$diff_id;
+    }
+
+    $path_hash = $this->getChangesetPathHash($changeset);
+    $changeset_phid = $this->getChangesetKey($changeset);
+
+    $this->hasModifications = true;
+
+    $this->viewState['changesets'][$path_hash][$key][$changeset_phid] =
+      $properties;
+  }
+
+  public function getChangesetProperty(
+    DifferentialChangeset $changeset,
+    $key,
+    $default = null) {
+
+    $path_hash = $this->getChangesetPathHash($changeset);
+
+    $entries = idxv($this->viewState, array('changesets', $path_hash, $key));
+    if (!is_array($entries)) {
+      $entries = array();
+    }
+
+    $entries = isort($entries, 'epoch');
+
+    $entry = last($entries);
+    if (!is_array($entry)) {
+      $entry = array();
+    }
+
+    return idx($entry, 'value', $default);
+  }
+
+  public function getHasModifications() {
+    return $this->hasModifications;
+  }
+
+  private function getChangesetPathHash(DifferentialChangeset $changeset) {
+    $path = $changeset->getFilename();
+    return PhabricatorHash::digestForIndex($path);
+  }
+
+  private function getChangesetKey(DifferentialChangeset $changeset) {
+    $key = $changeset->getID();
+
+    if ($key === null) {
+      return '*';
+    }
+
+    return (string)$key;
+  }
+
+  public static function copyViewStatesToObject($src_phid, $dst_phid) {
+    $table = new self();
+    $conn = $table->establishConnection('w');
+
+    queryfx(
+      $conn,
+      'INSERT IGNORE INTO %R
+          (viewerPHID, objectPHID, viewState, dateCreated, dateModified)
+        SELECT viewerPHID, %s, viewState, dateCreated, dateModified
+          FROM %R WHERE objectPHID = %s',
+      $table,
+      $dst_phid,
+      $table,
+      $src_phid);
+  }
+
+/* -(  PhabricatorPolicyInterface  )----------------------------------------- */
+
+
+  public function getCapabilities() {
+    return array(
+      PhabricatorPolicyCapability::CAN_VIEW,
+    );
+  }
+
+  public function getPolicy($capability) {
+    return PhabricatorPolicies::POLICY_NOONE;
+  }
+
+  public function hasAutomaticCapability($capability, PhabricatorUser $viewer) {
+    return ($viewer->getPHID() === $this->getViewerPHID());
+  }
+
+}
diff --git a/src/applications/differential/xaction/DifferentialRevisionUpdateTransaction.php b/src/applications/differential/xaction/DifferentialRevisionUpdateTransaction.php
--- a/src/applications/differential/xaction/DifferentialRevisionUpdateTransaction.php
+++ b/src/applications/differential/xaction/DifferentialRevisionUpdateTransaction.php
@@ -100,6 +100,14 @@
         HarbormasterMessageType::BUILDABLE_CONTAINER,
         true);
     }
+
+    // See T13455. If users have set view properites on a diff and the diff
+    // is then attached to a revision, attempt to copy their view preferences
+    // to the revision.
+
+    DifferentialViewState::copyViewStatesToObject(
+      $diff->getPHID(),
+      $object->getPHID());
   }
 
   public function getColor() {
diff --git a/src/applications/diffusion/controller/DiffusionDiffController.php b/src/applications/diffusion/controller/DiffusionDiffController.php
--- a/src/applications/diffusion/controller/DiffusionDiffController.php
+++ b/src/applications/diffusion/controller/DiffusionDiffController.php
@@ -60,9 +60,20 @@
       return new Aphront404Response();
     }
 
-    $parser = new DifferentialChangesetParser();
-    $parser->setUser($viewer);
-    $parser->setChangeset($changeset);
+    $commit = $drequest->loadCommit();
+
+    $viewstate_engine = id(new PhabricatorChangesetViewStateEngine())
+      ->setViewer($viewer)
+      ->setObjectPHID($commit->getPHID())
+      ->setChangeset($changeset);
+
+    $viewstate = $viewstate_engine->newViewStateFromRequest($request);
+
+    $parser = id(new DifferentialChangesetParser())
+      ->setViewer($viewer)
+      ->setChangeset($changeset)
+      ->setViewState($viewstate);
+
     $parser->setRenderingReference($drequest->generateURI(
       array(
         'action' => 'rendering-ref',
@@ -75,8 +86,6 @@
       $parser->setCoverage($coverage);
     }
 
-    $commit = $drequest->loadCommit();
-
     $pquery = new DiffusionPathIDQuery(array($changeset->getFilename()));
     $ids = $pquery->loadPathIDs();
     $path_id = $ids[$changeset->getFilename()];
diff --git a/src/infrastructure/diff/viewstate/PhabricatorChangesetViewState.php b/src/infrastructure/diff/viewstate/PhabricatorChangesetViewState.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/diff/viewstate/PhabricatorChangesetViewState.php
@@ -0,0 +1,17 @@
+<?php
+
+final class PhabricatorChangesetViewState
+  extends Phobject {
+
+  private $highlightLanguage;
+
+  public function setHighlightLanguage($highlight_language) {
+    $this->highlightLanguage = $highlight_language;
+    return $this;
+  }
+
+  public function getHighlightLanguage() {
+    return $this->highlightLanguage;
+  }
+
+}
diff --git a/src/infrastructure/diff/viewstate/PhabricatorChangesetViewStateEngine.php b/src/infrastructure/diff/viewstate/PhabricatorChangesetViewStateEngine.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/diff/viewstate/PhabricatorChangesetViewStateEngine.php
@@ -0,0 +1,145 @@
+<?php
+
+final class PhabricatorChangesetViewStateEngine
+  extends Phobject {
+
+  private $viewer;
+  private $objectPHID;
+  private $changeset;
+  private $storage;
+
+  public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  public function getViewer() {
+    return $this->viewer;
+  }
+
+  public function setObjectPHID($object_phid) {
+    $this->objectPHID = $object_phid;
+    return $this;
+  }
+
+  public function getObjectPHID() {
+    return $this->objectPHID;
+  }
+
+  public function setChangeset(DifferentialChangeset $changeset) {
+    $this->changeset = $changeset;
+    return $this;
+  }
+
+  public function getChangeset() {
+    return $this->changeset;
+  }
+
+  public function newViewStateFromRequest(AphrontRequest $request) {
+    $storage = $this->loadViewStateStorage();
+
+    $this->setStorage($storage);
+
+    $highlight = $request->getStr('highlight');
+    if ($highlight !== null && strlen($highlight)) {
+      $this->setChangesetProperty('highlight', $highlight);
+    }
+
+    $this->saveViewStateStorage();
+
+    $state = new PhabricatorChangesetViewState();
+
+    $highlight_language = $this->getChangesetProperty('highlight');
+    $state->setHighlightLanguage($highlight_language);
+
+    return $state;
+  }
+
+  private function setStorage(DifferentialViewState $storage) {
+    $this->storage = $storage;
+    return $this;
+  }
+
+  private function getStorage() {
+    return $this->storage;
+  }
+
+  private function setChangesetProperty(
+    $key,
+    $value) {
+
+    $storage = $this->getStorage();
+    $changeset = $this->getChangeset();
+
+    $storage->setChangesetProperty($changeset, $key, $value);
+  }
+
+  private function getChangesetProperty(
+    $key,
+    $default = null) {
+
+    $storage = $this->getStorage();
+    $changeset = $this->getChangeset();
+
+    return $storage->getChangesetProperty($changeset, $key, $default);
+  }
+
+  private function loadViewStateStorage() {
+    $viewer = $this->getViewer();
+
+    $object_phid = $this->getObjectPHID();
+    $viewer_phid = $viewer->getPHID();
+
+    $storage = null;
+
+    if ($viewer_phid !== null) {
+      $storage = id(new DifferentialViewStateQuery())
+        ->setViewer($viewer)
+        ->withViewerPHIDs(array($viewer_phid))
+        ->withObjectPHIDs(array($object_phid))
+        ->executeOne();
+    }
+
+    if ($storage === null) {
+      $storage = id(new DifferentialViewState())
+        ->setObjectPHID($object_phid);
+
+      if ($viewer_phid !== null) {
+        $storage->setViewerPHID($viewer_phid);
+      } else {
+        $storage->makeEphemeral();
+      }
+    }
+
+    return $storage;
+  }
+
+  private function saveViewStateStorage() {
+    if (PhabricatorEnv::isReadOnly()) {
+      return;
+    }
+
+    $storage = $this->getStorage();
+
+    $viewer_phid = $storage->getViewerPHID();
+    if ($viewer_phid === null) {
+      return;
+    }
+
+    if (!$storage->getHasModifications()) {
+      return;
+    }
+
+    $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+
+    try {
+      $storage->save();
+    } catch (AphrontDuplicateKeyQueryException $ex) {
+      // We may race another process to save view state. For now, just discard
+      // our state if we do.
+    }
+
+    unset($unguarded);
+  }
+
+}