Fix incorrect paint invalidations with accelerated 2D canvas

Fix incorrect paint invalidations with accelerated 2D canvas

In cases where a canvas is accelerated, its content are separated into
a compositor layer. When propagating invalidations through that layer,
invalidation rectangles need to be expressed relative to the layer's
origin, which is the top left corner of the canvas's content box.
Before this change, coordinates were relative to the canvas's layout
box, which is correct for non-accelerated cases.

BUG=490106
TEST=/fast/canvas/canvas-incremental-repaint-3.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=195817

[Justin Novosad, 2015-05-22 16:17:12]

junov@chromium.org changed reviewers:
+ senorblanco@chromium.org

[Justin Novosad, 2015-05-22 16:17:12]

PTAL

[Stephen White, 2015-05-22 20:26:58]

LGTM

[Justin Novosad, 2015-05-22 20:38:11]

The CQ bit was checked by junov@chromium.org

[commit-bot: I haz the power, 2015-05-22 20:38:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1149973006/20001

[commit-bot: I haz the power, 2015-05-22 23:07:50]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=195817