Re-enable layer squashing

We've fixed all the know bugs. Hopefully this time it will stick. If you find
that this CL caused a regression, please mark the bug as blocking
http://crbug.com/365701

BUG=365701

Review URL: https://codereview.chromium.org/267343005

git-svn-id: svn://svn.chromium.org/blink/trunk@173696 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Auto-rebaseline for r173666

http://src.chromium.org/viewvc/blink?view=revision&revision=173666

BUG=369609
TBR=enne@chromium.org

Review URL: https://codereview.chromium.org/278623003

git-svn-id: svn://svn.chromium.org/blink/trunk@173697 bbb929c8-8fbe-4397-9dbb-9b2b20218538