Get rid of hack in invalidatePaintUsingContainer for partially computed
squashing layer state. This is no longer necessary after crrev.com/311813005.

BUG=

Review URL: https://codereview.chromium.org/331563005

git-svn-id: svn://svn.chromium.org/blink/trunk@176138 bbb929c8-8fbe-4397-9dbb-9b2b20218538