Move WebLayerTreeView::NotifySwapTime to WebWidgetClient. (9/n)

The WebLayerTreeView is a shortcut past the WebWidgetClient that is
not needed now that we always composite. This works toward eliminating
this extra API layer.

More importantly this helps us Close/Restart the WebWidget parts of
WebViewImpl by not requiring plumbing 2 pointers with slightly different
lifetimes (WebLayerTreeView is created inside the Init of the
WebWidgetClient). This will help avoid a bunch of complexity in
creating WebFrameWidgets and other WebWidgets.

The RequestNewLayerTreeFrameSink() method is added to
CompositorDependencies so that RenderWidget unittests can run the
compositor without needing a real RenderThreadImpl.

[email protected], [email protected]

Bug: 912193
Change-Id: Ieae414387f347e065ab48f536c770e7c55f4d337
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1546148
Commit-Queue: danakj <[email protected]>
Auto-Submit: danakj <[email protected]>
Reviewed-by: Antoine Labour <[email protected]>
Reviewed-by: Philip Rogers <[email protected]>
Cr-Commit-Position: refs/heads/master@{#648341}
37 files changed