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}
IntRect PaintLayerScrollableArea::RectForHorizontalScrollbar(
    const IntRect& border_box_rect) const {
  if (!HasHorizontalScrollbar())
    return IntRect();

  const IntRect& scroll_corner = ScrollCornerRect();

  return IntRect(
      HorizontalScrollbarStart(border_box_rect.X()),
      border_box_rect.MaxY() - GetLayoutBox()->BorderBottom().ToInt() -
          HorizontalScrollbar()->ScrollbarThickness(),
      border_box_rect.Width() -
          (GetLayoutBox()->BorderLeft() + GetLayoutBox()->BorderRight())
              .ToInt() -
          scroll_corner.Width(),
      HorizontalScrollbar()->ScrollbarThickness());
}

IntRect PaintLayerScrollableArea::RectForHorizontalScrollbar(
    const IntRect& border_box_rect) const {
  if (!HasHorizontalScrollbar())
    return IntRect();

  const IntRect& scroll_corner = ScrollCornerRect();

  return IntRect(
      HorizontalScrollbarStart(border_box_rect.X()),
      border_box_rect.MaxY() - GetLayoutBox()->BorderBottom().ToInt() -
          HorizontalScrollbar()->ScrollbarThickness(),
      border_box_rect.Width() -
          (GetLayoutBox()->BorderLeft() + GetLayoutBox()->BorderRight())
              .ToInt() -
          scroll_corner.Width(),
      HorizontalScrollbar()->ScrollbarThickness());
}
