Add an heuristic for promoting canvases to GPU acceleration
This change adds a new condition under which 2D canvases should be
promoted to GPU acceleration: if a gpu-accelerated source is drawn to
it. There was a pre-existing heuristic for disabling acceleration on
the source if the source is a 2D canvas. Promoting the destination,
if possible, is usually preferable. This also has benefits when the
source is a WebGL canvas or a video.
BUG=464835, 524628
Review-Url: https://codereview.chromium.org/2625873005
Cr-Commit-Position: refs/heads/master@{#443923}
10 files changed
