Split TestWebViewClient and TestWebWidgetClient.

WebViewClient and WebWidgetClient no longer inherit each other, do the
same with these test overrides.

WebViewHelper takes a TestWebViewClient and if null makes one itself.
Similarly TestWebViewClient takes a TestWebWidgetClient, and if null
makes one itself. Then WebViewHelper gets the WebWidgetClient from
the WebViewClient, avoiding us having 2 channels for this object
through WebViewHelper.

R=dcheng@chromium.org

Change-Id: If9ba127bafc19a8a881c971aefdb25c201656d51
Bug: 912193
Reviewed-on: https://chromium-review.googlesource.com/c/1370720
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615669}
23 files changed