Make most file reads policy-aware

Summary: Ref T603. Swaps out most `PhabricatorFile` loads for `PhabricatorFileQuery`.

Test Plan:
  - Viewed Differential changesets.
  - Used `file.info`.
  - Used `file.download`.
  - Viewed a file.
  - Deleted a file.
  - Used `/Fnnnn` to access a file.
  - Uploaded an image, verified a thumbnail generated.
  - Created and edited a macro.
  - Added a meme.
  - Did old-school attach-a-file-to-a-task.
  - Viewed a paste.
  - Viewed a mock.
  - Embedded a mock.
  - Profiled a page.
  - Parsed a commit with image files linked to a revision with image files.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7178

src/applications/macro/controller/PhabricatorMacroMemeController.php

@@ -38,10 +38,15 @@ final class PhabricatorMacroMemeController
         $file->getPHID(), $hash);
 
     if ($xform) {
-      $memefile = id(new PhabricatorFile())->loadOneWhere(
-      'phid = %s', $xform->getTransformedPHID());
-      return $memefile->getBestURI();
+      $memefile = id(new PhabricatorFileQuery())
+        ->setViewer($user)
+        ->withPHIDs(array($xform->getTransformedPHID()))
+        ->executeOne();
+      if ($memefile) {
+        return $memefile->getBestURI();
+      }
     }
+
     $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
     $transformers = (new PhabricatorImageTransformer());
     $newfile = $transformers