Update main thread scrolling reasons when the frame view root layer changes.

A boolean condition got flipped in https://codereview.chromium.org/13838005. Put it back.

Tests are coming shortly when I reland this reverted patch https://codereview.chromium.org/40373002.

R=jamesr@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/65343008

git-svn-id: svn://svn.chromium.org/blink/trunk@161678 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Work on -Wunused-functions for linux.

BUG=315884
TBR=cevans

Review URL: https://codereview.chromium.org/66843007

git-svn-id: svn://svn.chromium.org/blink/trunk@161679 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove exceptions in core/platform/DEPS that no longer apply.

BUG=

Review URL: https://codereview.chromium.org/66193009

git-svn-id: svn://svn.chromium.org/blink/trunk@161680 bbb929c8-8fbe-4397-9dbb-9b2b20218538