Fix hang when dragging dialogs with the app list open.

Fix hang when dragging dialogs with the app list open.

For some reason, deleting a TopIconAnimationView in its animation completed
callback caused app list dialogs to hang when dragged. This CL defers the
deletion of the offending view which fixes this problem.

BUG=386555
TEST=On Windows, Open Chrome task manager and leave it open (note that the taskmanager
window can be dragged). Open app list, right-click an app, select uninstall and
leave that dialog open (note that the taskmanger window can still be dragged).
Now cancel uninstall dialog, expand an app list folder, select uninstall on an
app in that folder and leave that dialog open. Task manager window should still
be able to be dragged. (before this CL, the task manager could not be dragged in
the last case: mouse events were queued until `Esc` was pressed).

Review URL: https://codereview.chromium.org/418263002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286138 0039d316-1c4b-4281-b951-d872f2087c98