Make "Highlight As..." sticky across reloads in Diffusion and Differential

Summary:
Ref T13455. Add container-level storage for persistent view state, and persist "Highlight As..." inside it.

The storage generates a "PhabricatorChangesetViewState" configuration object as an output.

When preferences are expressed on a diff and that diff is later attached to a revision, we attempt to copy the preferences.

The internal storage tracks per-changeset settings, but currently always uses "last update wins" to apply the settings in the UI.

Test Plan:
  - Viewed revisions, changed highlighting, reloaded. Saw highlighting stick in revision view and standalone view.
  - Viewed commits, changed highlighting, reloaded. Saw highlighting stick.
  - Created a diff, changed highlighting, turned it into a revision, saw highlighting persist.

Subscribers: jmeador, PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13455

Differential Revision: https://secure.phabricator.com/D21137

src/applications/differential/controller/DifferentialChangesetViewController.php

@@ -165,21 +165,6 @@ final class DifferentialChangesetViewController extends DifferentialController {
     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 @@ final class DifferentialChangesetViewController extends DifferentialController {
       }
     }
 
+    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 @@ final class DifferentialChangesetViewController extends DifferentialController {
     $engine->process();
 
     $parser
-      ->setUser($viewer)
+      ->setViewer($viewer)
       ->setMarkupEngine($engine)
       ->setShowEditAndReplyLinks(true)
       ->setCanMarkDone($can_mark)