Canvas: Fix potential assertion hit.

This CL applies WebGL change in r172564 to Accelerated 2D Canvas.

BUG=322335

Review URL: https://codereview.chromium.org/259963003

git-svn-id: svn://svn.chromium.org/blink/trunk@172901 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove scroll bars from animated-path-inside-transformed-html.xhtml

Modify the test to remove scrollbars so we don't test the scrollbar
pixel output in this test: rotate the box by 10deg.

BUG=367653,367846

Review URL: https://codereview.chromium.org/256873006

git-svn-id: svn://svn.chromium.org/blink/trunk@172902 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add devtools trace event for Timeline Paint notification

BUG=361045

Review URL: https://codereview.chromium.org/251263003

git-svn-id: svn://svn.chromium.org/blink/trunk@172903 bbb929c8-8fbe-4397-9dbb-9b2b20218538