Always call UpdateCompositedScrollOffset, not just for the root layer

Bug: 927560
Change-Id: I1d5522aae4f11dd3f5b8947bb089bac1bf19bdb4
Reviewed-on: https://chromium-review.googlesource.com/c/1452701
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628942}
bool PaintLayerScrollableArea::ShouldScrollOnMainThread() const {
  if (HasBeenDisposed())
    return true;
  if (LocalFrame* frame = GetLayoutBox()->GetFrame()) {
    if (frame->View()->GetMainThreadScrollingReasons())
      return true;
  }
  if (HasNonCompositedStickyDescendants())
    return true;
  return ScrollableArea::ShouldScrollOnMainThread();
}

bool PaintLayerScrollableArea::ShouldScrollOnMainThread() const {
  if (HasBeenDisposed())
    return true;
  if (LocalFrame* frame = GetLayoutBox()->GetFrame()) {
    if (frame->View()->GetMainThreadScrollingReasons())
      return true;
  }
  if (HasNonCompositedStickyDescendants())
    return true;
  return ScrollableArea::ShouldScrollOnMainThread();
}
