Pinch/Zoom Infrastructure & Plumbing CL

cc/trees/tree_synchronizer.cc

Index: cc/trees/tree_synchronizer.cc
diff --git a/cc/trees/tree_synchronizer.cc b/cc/trees/tree_synchronizer.cc
index 27f9dab38d868f9d5a82a661b7d21481fa2360f8..1c1c7e164ad00244f0faa253432ccde7fc497202 100644
--- a/cc/trees/tree_synchronizer.cc
+++ b/cc/trees/tree_synchronizer.cc
@@ -25,6 +25,13 @@ void CollectExistingLayerImplRecursive(ScopedPtrLayerImplMap* old_layers,
   if (!layer_impl)
     return;
 
+  layer_impl->ClearScrollbars();
+  if (ScrollbarLayerImplBase* scrollbar_layer =
+          layer_impl->ToScrollbarLayer()) {
+    scrollbar_layer->ClearClipLayer();
+    scrollbar_layer->ClearScrollLayer();
+  }
+
   OwnedLayerImplList& children = layer_impl->children();
   for (OwnedLayerImplList::iterator it = children.begin();
        it != children.end();
@@ -112,11 +119,6 @@ scoped_ptr<LayerImpl> SynchronizeTreesRecursiveInternal(
   layer_impl->SetReplicaLayer(SynchronizeTreesRecursiveInternal(
       new_layers, old_layers, layer->replica_layer(), tree_impl));
 
-  // Remove all dangling pointers. The pointers will be setup later in
-  // UpdateScrollbarLayerPointersRecursive phase
-  layer_impl->SetHorizontalScrollbarLayer(NULL);
-  layer_impl->SetVerticalScrollbarLayer(NULL);
-
   return layer_impl.Pass();
 }
 
@@ -160,17 +162,9 @@ void UpdateScrollbarLayerPointersRecursiveInternal(
       iter != new_layers->end()
           ? static_cast<ScrollbarLayerImplBase*>(iter->second)
           : NULL;
-  iter = new_layers->find(scrollbar_layer->ScrollLayerId());
-  LayerImpl* scroll_layer_impl =
-      iter != new_layers->end() ? iter->second : NULL;
-
   DCHECK(scrollbar_layer_impl);
-  DCHECK(scroll_layer_impl);
 
-  if (scrollbar_layer->orientation() == HORIZONTAL)
-    scroll_layer_impl->SetHorizontalScrollbarLayer(scrollbar_layer_impl);
-  else
-    scroll_layer_impl->SetVerticalScrollbarLayer(scrollbar_layer_impl);
+  scrollbar_layer->PushScrollClipPropertiesTo(scrollbar_layer_impl);
 }
 
 void UpdateScrollbarLayerPointersRecursive(const RawPtrLayerImplMap* new_layers,
@@ -205,6 +199,8 @@ void TreeSynchronizer::PushPropertiesInternal(
 
   if (push_layer)
     layer->PushPropertiesTo(layer_impl);
+  else if (layer->ToScrollbarLayer())
+    layer->ToScrollbarLayer()->PushScrollClipPropertiesTo(layer_impl);
 
   size_t num_dependents_need_push_properties = 0;
   if (recurse_on_children_and_dependents) {