When the profiler is active, keep it active if the user submits forms
Summary: Ref T12297. When a page is generated with the profiler active, keep it active by adding a __profile__ input to any forms we generate.
Test Plan: Hit Conduit API page with __profile__ active, saw it reflected in forms.
Reviewed By: chad
Maniphest Tasks: T12297
Differential Revision: https://secure.phabricator.com/D17399