Use will-change: auto !important in fullscreen.css

will-change: none doesn't actually work, and the original problem with
http://output.jsbin.com/wimura was not fixed by
https://codereview.chromium.org/1656713002

The test case is modified to match the original problem, so that this
doesn't regress with the top layer rewrite.

BUG=582318,240576
R=eae@chromium.org,esprehn@chromium.org

Review-Url: https://codereview.chromium.org/2131283002
Cr-Commit-Position: refs/heads/master@{#404851}
2 files changed