[Webview] Refactor AutoResize handling into Webview.

This CL moves WebContents AutoResizing behavior into Webview rather than
handling it in subclasses of Webview. This will enable the addition of
other AutoResizing Webviews without the need for a custom subclass.

Bug: 849551
Change-Id: I2a31a57180ff43b6cda9827ba9d19dcddcd1db24
Reviewed-on: https://chromium-review.googlesource.com/1127216
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576404}
4 files changed