Remove attach_ as publicly exposed method of Event.

BUG=324859

Review URL: https://codereview.chromium.org/139903006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247899 0039d316-1c4b-4281-b951-d872f2087c98

chrome/renderer/resources/extensions/event.js

@@ -519,7 +519,6 @@
     'getRules',
     // TODO(fsamuel): We really shouldn't be exposing these private methods
     // but certain tests rely on them.
-    'attach_',
     'dispatch_'
   ]);