Paint overlay resizer in the dedicated paint phase. (2/3)

Clean up PaintLayerScrollableArea::UpdateScrollCornerStyle and
ScrollableAreaPainter::PaintResizer with the new added function:
PaintLayerScrollableArea::HasNonOverlayOverflowControls.

This is 2/3 of a series of patches:
  1. https://crrev.com/c/1816486
  2. This patch.
  3. https://crrev.com/c/1831917

Bug: 1006173
Change-Id: Ic6bb659cb7d7e646955e08a4f5035313f71dee01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817874Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705418}

third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc

@@ -1689,8 +1689,7 @@ void PaintLayerScrollableArea::PositionOverflowControls() {
 }
 
 void PaintLayerScrollableArea::UpdateScrollCornerStyle() {
-  bool can_update = HasScrollbar() && !HasOverlayScrollbars();
-  if (!can_update) {
+  if (!HasNonOverlayOverflowControls()) {
     if (scroll_corner_) {
       scroll_corner_->Destroy();
       scroll_corner_ = nullptr;

third_party/blink/renderer/core/paint/scrollable_area_painter.cc

@@ -64,8 +64,7 @@ void ScrollableAreaPainter::PaintResizer(GraphicsContext& context,
 
   // Draw a frame around the resizer (1px grey line) if there are any scrollbars
   // present.  Clipping will exclude the right and bottom edges of this frame.
-  if (!GetScrollableArea().HasOverlayScrollbars() &&
-      GetScrollableArea().HasScrollbar()) {
+  if (GetScrollableArea().HasNonOverlayOverflowControls()) {
     GraphicsContextStateSaver state_saver(context);
     context.Clip(abs_rect);
     IntRect larger_corner = abs_rect;