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Threaded scrolls unnecessarily cause commits on every change. This
patch implements an optimization from pre-BlinkGenPropertyTrees in
layer list mode to avoid these commits.

When an impl-side scroll occurs, cc can immediately apply the scroll
before notifying blink so that the blink update only causes a commit if
needed (e.g., interest rect changed). This has been implemented in
LayerTreeHost::UpdateScrollOffsetFromImpl. A second change was needed in
PropertyTreeManager::DirectlyUpdateScrollOffsetTransform to avoid
commits if cc already matches blink.

This is a reland of https://crrev.com/745110.

Bug: 1048384f
Change-Id: Id50a0d0a944f7d1f763906304bbcfccdf81cb301
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2297709
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790598}