[RootLayerScrolls] Don't use LocalFrameView as a ScrollableArea

Delete a bunch of places where LocalFrameView is used as a
a ScrollableArea. In many places, the code is no-op and can be
deleted; in other places, migrate to methods that are not declared
on ScrollableArea.

BUG=823365
R=skobes@chromium.org,pdr@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ifefb7676b6501ca1ec42bb5a7339a762023e4f96
Reviewed-on: https://chromium-review.googlesource.com/1119771
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571697}
22 files changed