Move VideoDestinationHandler processing to the IO-thread.
This moves reading video frames from shared memory memory received from the pepper effects plugin to the IO thread.
Also RGBA color conversion is now done on the IO thread.
The purpose of this is to free up processing time on the main render thread. Note that, before this change, the frames from the plugin was posted to the IO thread after the color conversion was done.

BUG= 421554

Review URL: https://codereview.chromium.org/631903003

Cr-Commit-Position: refs/heads/master@{#298885}
5 files changed