Picture-in-Picture: send window size updates.

Implements a callback mechanism to notify the blink
PictureInPictureWindow when the //content/browser window's size has
changed.

Bug: 806249
Change-Id: I5a110e64ab2762f28d963a15790d842b9f6e126c
Reviewed-on: https://chromium-review.googlesource.com/1068066
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561633}
25 files changed