Revert "[PiP v2] EnterPictureInPicture should return result"

This reverts commit 05df70856d90ad4560c2f39c2c35f297c0f5a4d1.

Reason for revert:
causing unit test failure:
https://ci.chromium.org/p/chromium/builders/ci/Cast%20Linux/75181

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 <avi@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
> Commit-Queue: Becca Hughes <beccahughes@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#666760}

TBR=avi@chromium.org,mlamouri@chromium.org,jochen@chromium.org,beccahughes@chromium.org

Change-Id: Ib86e3635f4ca039de1474ee9bc6758a3da8047a3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 953957
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1647725
Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666773}