Reland "[PiP v2] EnterPictureInPicture should return result"

This is a reland of 05df70856d90ad4560c2f39c2c35f297c0f5a4d1

Original change's description:
> [PiP v2] EnterPictureInPicture should return result
>
> Instead of returning the window size from EnterPictureInPicture
> we return a result enum as to whether the request was successful.
>
> We don't need to return the window size because we already have
> that in content.
>
> BUG=953957
>
> Change-Id: I982433de29f1ef4f13f4db24fdefd5f4f5e86d32
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623464
> Reviewed-by: Avi Drissman <[email protected]>
> Reviewed-by: Jochen Eisinger <[email protected]>
> Reviewed-by: Mounir Lamouri <[email protected]>
> Commit-Queue: Becca Hughes <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#666760}

Bug: 953957
Change-Id: I02648d139b474ed6ef43cb06bf63fb9903f6cdca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1649188
Reviewed-by: Jochen Eisinger <[email protected]>
Reviewed-by: Mounir Lamouri <[email protected]>
Commit-Queue: Becca Hughes <[email protected]>
Cr-Commit-Position: refs/heads/master@{#668028}
35 files changed