RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollb…

Source/platform/scroll/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 301 matching lines @@
 }
 
 void ScrollableArea::contentsResized()
 {
     if (ScrollAnimator* scrollAnimator = existingScrollAnimator())
         scrollAnimator->contentsResized();
 }
 
 bool ScrollableArea::hasOverlayScrollbars() const
 {
-    return (verticalScrollbar() && verticalScrollbar()->isOverlayScrollbar())
-        || (horizontalScrollbar() && horizontalScrollbar()->isOverlayScrollbar());
+    Scrollbar* vScrollbar = verticalScrollbar();
+    if (vScrollbar && vScrollbar->isOverlayScrollbar())
+        return true;
+    Scrollbar* hScrollbar = horizontalScrollbar();
+    return hScrollbar && hScrollbar->isOverlayScrollbar();
 }
 
 void ScrollableArea::setScrollbarOverlayStyle(ScrollbarOverlayStyle overlayStyle)
 {
     m_scrollbarOverlayStyle = overlayStyle;
 
-    if (horizontalScrollbar()) {
-        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(horizontalScrollbar());
-        horizontalScrollbar()->invalidate();
+    if (Scrollbar* scrollbar = horizontalScrollbar()) {
+        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
+        scrollbar->invalidate();
     }
 
-    if (verticalScrollbar()) {
-        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(verticalScrollbar());
-        verticalScrollbar()->invalidate();
+    if (Scrollbar* scrollbar = verticalScrollbar()) {
+        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
+        scrollbar->invalidate();
     }
 }
 
 void ScrollableArea::invalidateScrollbar(Scrollbar* scrollbar, const IntRect& rect)
 {
     if (scrollbar == horizontalScrollbar()) {
         if (GraphicsLayer* graphicsLayer = layerForHorizontalScrollbar()) {
             graphicsLayer->setNeedsDisplay();
             graphicsLayer->setContentsNeedsDisplay();
             return;
@@ skipping 70 matching lines @@
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace WebCore