[Picture-in-Picture] Use DCHECK in IsPictureInPictureElement.

Since element passed to IsPictureInPictureElement shouldn't be null, we
can use a DCHECK instead of a simple "if" condition.

Bug: 806249
Change-Id: I0babdc26569a37ebaae2bbc6f39e4cd00da0beb3
Reviewed-on: https://chromium-review.googlesource.com/1086787
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#564383}
1 file changed