GitLab

The canvas() is now only accessed through the Recorder classes (ie.
PaintRecorder and friends).  Now we can put a DisplayItemList instead
of a Canvas inside PaintContext.

R=piman@chromium.org
BUG=466426

Review URL: https://codereview.chromium.org/1069183002

Cr-Commit-Position: refs/heads/master@{#324210}