GitLab

Adds interface BackgroundThumbnailCapturer for capturing background
tabs. The current video capture logic is moved to implementation
BackgroundThumbnailVideoCapturer.

This will allow experimenting with different capture techniques.

Bug: 1090038
Change-Id: I6204f767be6c8bf42aebf79ca0f9e24606d91f70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2561466Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834465}