Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/layer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layer.h"
 
 #include "cc/animation.h"
 #include "cc/animation_events.h"
 #include "cc/layer_animation_controller.h"
 #include "cc/layer_impl.h"
@@ skipping 378 matching lines @@
   if (opacity_ == opacity)
     return;
   opacity_ = opacity;
   SetNeedsCommit();
 }
 
 bool Layer::OpacityIsAnimating() const {
   return layer_animation_controller_->IsAnimatingProperty(Animation::Opacity);
 }
 
+bool Layer::DoNotSkipOnZeroOpacity() const {
+  return false;
+}
+
 void Layer::SetContentsOpaque(bool opaque) {
   if (contents_opaque_ == opaque)
     return;
   contents_opaque_ = opaque;
   SetNeedsCommit();
 }
 
 void Layer::SetPosition(gfx::PointF position) {
   if (position_ == position)
     return;
@@ skipping 393 matching lines @@
   if (contents_opaque())
     return visible_content_rect();
   return Region();
 }
 
 ScrollbarLayer* Layer::ToScrollbarLayer() {
   return NULL;
 }
 
 }  // namespace cc