Don't show Phriction draft edit events in feed

Summary: Depends on D19663. Ref T13077. When you edit a Phriction draft, don't publish a feed story. (The eventual "Publish" event gets a story.)

Test Plan: Made draft / non-draft / publish edits, only saw feed stories for non-draft and publish edits.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13077

Differential Revision: https://secure.phabricator.com/D19664

src/applications/phriction/xaction/PhrictionDocumentDraftTransaction.php

@@ -11,6 +11,10 @@ final class PhrictionDocumentDraftTransaction
     $this->getEditor()->setShouldPublishContent($object, false);
   }
 
+  public function shouldHideForFeed() {
+    return true;
+  }
+
   public function validateTransactions($object, array $xactions) {
     $errors = array();