Use assert_instances_of() everywhere but Differential and Diffusion

Summary: NOTE: This is not produced by a script so there might be errors. Please review carefully.

Test Plan: Browse around.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2091

src/applications/phriction/controller/diff/PhrictionDiffController.php

@@ -233,6 +233,7 @@ final class PhrictionDiffController
   }
 
   private function renderComparisonTable(array $content) {
+    assert_instances_of($content, 'PhrictionContent');
 
     $user = $this->getRequest()->getUser();