This CL makes CompositorFrameSinkSupport into a
mojom::CompositorFrameSink. CompositorFrameSinkSupport already
implements the interface so this is a trivial change.

This CL also replaces CompositorFrameSinkSupportClient with
mojom::CompositorFrameSinkClient. The two interfaces were almost
identical, minus WillDrawSurface() method, which was only used in
DelegatedFrameHost. WillDrawSurface() is replaced with a callback.

This simplifies [Root]CompostiorFrameSinkImpl.  CompositorFrameSinkImpl
only needs to hold the Binding/InterfacePtr and delegate calls into
CompositorFrameSinkSupport. The client can be passed in directly.

This CL also cleans up test implementations of
CompositorFrameSink[Support]Client.

Bug: 762743
TBR: weiliangc@chromium.org
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ib4f1fd6a22badce9ae77a7bb484c6ab465e4d7c5
Reviewed-on: https://chromium-review.googlesource.com/641990


Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501313}