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

cc/tree_synchronizer.cc

 // Copyright 2011 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/tree_synchronizer.h"
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "cc/layer.h"
 #include "cc/layer_impl.h"
@@ skipping 130 matching lines @@
     LayerType* layer) {
   if (!layer)
     return;
 
   for (size_t i = 0; i < layer->children().size(); ++i) {
     UpdateScrollbarLayerPointersRecursiveInternal<
         LayerType, ScrollbarLayerType>(new_layers, layer->child_at(i));
   }
 
   ScrollbarLayerType* scrollbar_layer = layer->ToScrollbarLayer();
-  if (!scrollbar_layer)
+  // Pinch-zoom scrollbars will have an invalid scrollLayerId, but they are
+  // managed by LayerTreeImpl and not LayerImpl, so should not be
+  // processed here.
+  if (!scrollbar_layer || (scrollbar_layer->scroll_layer_id() ==
+                          Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID))
     return;
 
   RawPtrLayerImplMap::const_iterator iter =
       new_layers->find(scrollbar_layer->id());
   ScrollbarLayerImpl* scrollbar_layer_impl =
       iter != new_layers->end() ? static_cast<ScrollbarLayerImpl*>(iter->second)
                                : NULL;
   iter = new_layers->find(scrollbar_layer->scroll_layer_id());
   LayerImpl* scroll_layer_impl =
       iter != new_layers->end() ? iter->second : NULL;
@@ skipping 42 matching lines @@
 
 void TreeSynchronizer::PushProperties(Layer* layer, LayerImpl* layer_impl) {
   PushPropertiesInternal(layer, layer_impl);
 }
 
 void TreeSynchronizer::PushProperties(LayerImpl* layer, LayerImpl* layer_impl) {
   PushPropertiesInternal(layer, layer_impl);
 }
 
 }  // namespace cc