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 97 matching lines @@
 template <typename LayerType, typename ScrollbarLayerType>
 void updateScrollbarLayerPointersRecursiveInternal(const RawPtrLayerImplMap& newLayers, LayerType* layer)
 {
     if (!layer)
         return;
 
     for (size_t i = 0; i < layer->children().size(); ++i)
         updateScrollbarLayerPointersRecursiveInternal<LayerType, ScrollbarLayerType>(newLayers, layer->child_at(i));
 
     ScrollbarLayerType* scrollbarLayer = layer->ToScrollbarLayer();
-    if (!scrollbarLayer)
+    // Pinch-zoom scrollbars will have an invalid scrollLayerId, but they are
+    // managed by LayerTreeImpl and not LayerImpl, so should not be
+    // processed here.
+    if (!scrollbarLayer || (scrollbarLayer->scroll_layer_id() == Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID))
         return;
 
     RawPtrLayerImplMap::const_iterator iter = newLayers.find(scrollbarLayer->id());
     ScrollbarLayerImpl* scrollbarLayerImpl = iter != newLayers.end() ? static_cast<ScrollbarLayerImpl*>(iter->second) : NULL;
     iter = newLayers.find(scrollbarLayer->scroll_layer_id());
     LayerImpl* scrollLayerImpl = iter != newLayers.end() ? iter->second : NULL;
 
     DCHECK(scrollbarLayerImpl);
     DCHECK(scrollLayerImpl);
 
@@ skipping 40 matching lines @@
     pushPropertiesInternal(layer, layerImpl);
 }
 
 void TreeSynchronizer::pushProperties(LayerImpl* layer, LayerImpl* layerImpl)
 {
     pushPropertiesInternal(layer, layerImpl);
 }
 
 
 }  // namespace cc