Add constant full page raster + scroll + checkerboard test

We don't currently handle constant full page invalidations
very well while scrolling and checkerboard a ton.

This test will help track upcoming checkerboarding
improvements and make sure we don't regress this particular
devil case.

BUG=486072

Review URL: https://codereview.chromium.org/1268233004

Cr-Commit-Position: refs/heads/master@{#342658}
2 files changed