WebContentsVideoCapture Cleanup: Gut-out dead code, and tighten BUILDs.
Removes a bunch of dead code that was relevant years ago before Chromium
even had a compositor, including a capture from the "backing store" and
a separate "render thread" for scaling and YUV conversion. Also,
gutted-out and simplified the unit tests.
In addition, BUILD files were modified so that only the platforms that
have implementation build/link the relevant modules.
BUG=159234
Review-Url: https://codereview.chromium.org/2605973002
Cr-Commit-Position: refs/heads/master@{#441288}
6 files changed
