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/files/controller/PhabricatorFileDeleteController.php

@@ -9,13 +9,18 @@ final class PhabricatorFileDeleteController extends PhabricatorFileController {
   }
 
   public function processRequest() {
-
     $request = $this->getRequest();
     $user = $request->getUser();
 
-    $file = id(new PhabricatorFile())->loadOneWhere(
-      'id = %d',
-      $this->id);
+    $file = id(new PhabricatorFileQuery())
+      ->setViewer($user)
+      ->withIDs(array($this->id))
+      ->requireCapabilities(
+        array(
+          PhabricatorPolicyCapability::CAN_VIEW,
+          PhabricatorPolicyCapability::CAN_EDIT,
+        ))
+      ->executeOne();
     if (!$file) {
       return new Aphront404Response();
     }