Add non-blocking frame rate limiting logic to display list 2D canvas

This patch inserts frame barriers at the end of script execution tasks
that draw to a canvas. This is to prevent the accumulation of a multi-
frame backlog of draw commands in the SkPicture used by the display
list canvas implementation.

BUG=397516
TEST=RecordingImageBufferSurface unit tests

Review URL: https://codereview.chromium.org/429643002

git-svn-id: svn://svn.chromium.org/blink/trunk@179175 bbb929c8-8fbe-4397-9dbb-9b2b20218538