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}
void PaintLayerScrollableArea::ScrollbarManager::DestroyDetachedScrollbars() {
  DCHECK(!h_bar_is_attached_ || h_bar_);
  DCHECK(!v_bar_is_attached_ || v_bar_);
  if (h_bar_ && !h_bar_is_attached_)
    DestroyScrollbar(kHorizontalScrollbar);
  if (v_bar_ && !v_bar_is_attached_)
    DestroyScrollbar(kVerticalScrollbar);
}

void PaintLayerScrollableArea::ScrollbarManager::DestroyDetachedScrollbars() {
  DCHECK(!h_bar_is_attached_ || h_bar_);
  DCHECK(!v_bar_is_attached_ || v_bar_);
  if (h_bar_ && !h_bar_is_attached_)
    DestroyScrollbar(kHorizontalScrollbar);
  if (v_bar_ && !v_bar_is_attached_)
    DestroyScrollbar(kVerticalScrollbar);
}
