Disable overlay scrollbars in Blink when hidden by the compositor.
This patch adds and plumbs through a one-way notification from the compositor's
impl thread to Blink. This is used to prevent Blink from handling user input on
Scrollbars in cases where they've been hidden, as happens when overlay
scrollbars remain idle for a small amount of time. This patch makes use of this
setting when fading out scrollbars on the compositor but this will also be used
in Blink when scrollbars are faded-out there for non-composited scrollers. This
should have no visible effect for anything but Aura overlay scrollbars.
BUG=652826
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
Review-Url: https://codereview.chromium.org/2453553003
Cr-Commit-Position: refs/heads/master@{#428628}
29 files changed
