Fixed NPE when trying to animate a windows whose display is gone.

In some cases it is possible for the AppToken.allAppWindows list to
get out of sync with the list of windows known to WMS if the client
doesn't call Session.remove(Window). This can lead to an NPE when
the animation threads runs and the display for the window has been
removed.

Also corrected some method names/scopes I ran across while debugging.

Bug: 19972099
Change-Id: Ib0ae7ede6c506f833bbdd66723b88e7504a61907