Clean up WindowEventDispatcher some more.

. Eliminate the implementation of LayerAnimationObserver. It seems no one expects WED to be a LAO anymore.
. Remove WindowTreeHostDelegate. This involves moving some of the functions to WTH, removing some completely, and moving the remainder to the WED public API. A little icky for now, but I plan to take a pass on cleaning up WED's public API once I get it pared down.
. window_tree_host_x11_unittest provided an implementation of WTHD that was not WED. This is not a valid situation now since various functions in WTH now call directly through to WED. Replaced this with a simple EventHandler to test that events are being dispatched.

R=sky@chromium.org
http://crbug.com/308843

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255368

Review URL: https://codereview.chromium.org/188223002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255533 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255533