Provide the document content as a context object when rendering Phriction documents

Summary: Ref T13077. The context object wasn't being passed into the engine properly here, affecting relative link rendering in Phriction.

Test Plan: Viewed rendered Phriction documents with relative links, got clean renders.

Maniphest Tasks: T13077

Differential Revision: https://secure.phabricator.com/D19115

src/applications/phriction/storage/PhrictionContent.php

@@ -54,6 +54,7 @@ final class PhrictionContent
 
   public function newRemarkupView(PhabricatorUser $viewer) {
     return id(new PHUIRemarkupView($viewer, $this->getContent()))
+      ->setContextObject($this)
       ->setRemarkupOption(PHUIRemarkupView::OPTION_GENERATE_TOC, true)
       ->setGenerateTableOfContents(true);
   }