Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 782 matching lines @@
   // needs the m_has3DTransformedDescendant set.
   if (preserves3D())
     return has3DTransform() || m_has3DTransformedDescendant;
 
   return has3DTransform();
 }
 
 void PaintLayer::updateLayerPosition() {
   LayoutPoint localPoint;
 
+  bool didResize = false;
   if (layoutObject()->isInline() && layoutObject()->isLayoutInline()) {
     LayoutInline* inlineFlow = toLayoutInline(layoutObject());
     IntRect lineBox = enclosingIntRect(inlineFlow->linesBoundingBox());
     m_size = lineBox.size();
   } else if (LayoutBox* box = layoutBox()) {
-    m_size = pixelSnappedIntSize(box->size(), box->location());
+    IntSize newSize = pixelSnappedIntSize(box->size(), box->location());
+    didResize = newSize != m_size;
+    m_size = newSize;
     localPoint.moveBy(box->topLeftLocation());
   }
 
   if (!layoutObject()->isOutOfFlowPositioned() &&
       !layoutObject()->isColumnSpanAll() && layoutObject()->parent()) {
     // We must adjust our position by walking up the layout tree looking for the
     // nearest enclosing object with a layer.
     LayoutObject* curr = layoutObject()->parent();
     while (curr && !curr->hasLayer()) {
       if (curr->isBox() && !curr->isTableRow()) {
@@ skipping 37 matching lines @@
     LayoutSize newOffset = layoutObject()->offsetForInFlowPosition();
     if (m_rareData || !newOffset.isZero())
       ensureRareData().offsetForInFlowPosition = newOffset;
     localPoint.move(newOffset);
   } else if (m_rareData) {
     m_rareData->offsetForInFlowPosition = LayoutSize();
   }
 
   m_location = localPoint;
 
+  if (m_scrollableArea && didResize)
+    m_scrollableArea->visibleSizeChanged();
+
 #if DCHECK_IS_ON()
   m_needsPositionUpdate = false;
 #endif
 }
 
 TransformationMatrix PaintLayer::perspectiveTransform() const {
   if (!layoutObject()->hasTransformRelatedProperty())
     return TransformationMatrix();
 
   const ComputedStyle& style = layoutObject()->styleRef();
@@ skipping 2390 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif