Revert "Fix border-radius clip with composited scrolling."

Speculative revert to fix SyncErrorNotifierTest.PassphraseNotification.
This reverts commit r173970. See bug for details.

BUG=372973
TBR=hartmanng@chromium.org

Review URL: https://codereview.chromium.org/286673002

git-svn-id: svn://svn.chromium.org/blink/trunk@173985 bbb929c8-8fbe-4397-9dbb-9b2b20218538