Disable Compositor Driven Accelerated Overflow Scroll.

This should effectively disable the feature that was enabled in
https://codereview.chromium.org/20103002/ so we have time to fix
some bugs.

BUG=
R=vollick@chromium.org

Review URL: https://codereview.chromium.org/26520003

git-svn-id: svn://svn.chromium.org/blink/trunk@159360 bbb929c8-8fbe-4397-9dbb-9b2b20218538