Remove WebViewClient::WidgetClient()

There need not be a WebWidget{Client} for a WebView in the future, so
we must ensure code that is for views does not rely on there being a
widget. To aid this you can no longer get a WebWidgetClient from a
WebViewClient.

Most of this change is for frame_test_helpers to pass in these two
things separately again. And then move the LayerTreeView from the
TestWebViewClient to the TestWebWidgetClient.

R=dcheng@chromium.org
TBR=avi

Change-Id: I9cac9dae2ca8abc98a71c603bdacdbf62129a222
Bug: 912193
Reviewed-on: https://chromium-review.googlesource.com/c/1389320
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620748}
28 files changed