GitLab

Move tough_canvas_cases into rendering folder and refactor page classes
to inherit from RenderingStory.

Bug: 760553
Change-Id: I5cc1a745360968757569b1868be2fb3ddca7222c
Reviewed-on: https://chromium-review.googlesource.com/1078934
Commit-Queue: Amy Qiu <amyqiu@google.com>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#563010}