cc : Push layer lists instead of layer tree at commit and activation

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 901bba6175af8ffa1d92ac9e1d84987840ffa00d..56d1f5d212331105dd47fbd27d6250a708e0b9c0 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -261,11 +261,24 @@ void LayerTreeImpl::SetRootLayer(std::unique_ptr<LayerImpl> layer) {
   layer_tree_host_impl_->OnCanDrawStateChangedForTree();
 }
 
-void LayerTreeImpl::BuildLayerListForTesting() {
+void LayerTreeImpl::SetRootLayerFromLayerList() {

[jaydasika, 2016/06/09 05:07:54]

This needs better name! root_layer_ should ultimately be removed, but that
should be a different CL.

+  root_layer_ = layer_list_.empty() ? nullptr : layer_list_[0];
+  layer_tree_host_impl_->OnCanDrawStateChangedForTree();
+}
+
+void LayerTreeImpl::AddToLayerList(LayerImpl* layer) {
+  layer_list_.push_back(layer);
+}
+
+void LayerTreeImpl::ClearLayerList() {
   layer_list_.clear();
+}
+
+void LayerTreeImpl::BuildLayerListForTesting() {
+  ClearLayerList();
   LayerListIterator<LayerImpl> it(root_layer_);
   for (; it != LayerListIterator<LayerImpl>(nullptr); ++it) {
-    layer_list_.push_back(*it);
+    AddToLayerList(*it);
   }
 }
 
@@ -307,6 +320,7 @@ gfx::ScrollOffset LayerTreeImpl::TotalMaxScrollOffset() const {
 
 std::unique_ptr<OwnedLayerImplList> LayerTreeImpl::DetachLayers() {
   root_layer_ = nullptr;
+  layer_list_.clear();
   render_surface_layer_list_.clear();
   set_needs_update_draw_properties();
   std::unique_ptr<OwnedLayerImplList> ret = std::move(layers_);
@@ -444,20 +458,20 @@ void LayerTreeImpl::MoveChangeTrackingToLayers() {
   }
 }
 
-LayerListIterator<LayerImpl> LayerTreeImpl::begin() const {
-  return LayerListIterator<LayerImpl>(root_layer_);
+std::vector<LayerImpl*>::const_iterator LayerTreeImpl::begin() const {
+  return layer_list_.cbegin();
 }
 
-LayerListIterator<LayerImpl> LayerTreeImpl::end() const {
-  return LayerListIterator<LayerImpl>(nullptr);
+std::vector<LayerImpl*>::const_iterator LayerTreeImpl::end() const {
+  return layer_list_.cend();
 }
 
-LayerListReverseIterator<LayerImpl> LayerTreeImpl::rbegin() {
-  return LayerListReverseIterator<LayerImpl>(root_layer_);
+std::vector<LayerImpl*>::reverse_iterator LayerTreeImpl::rbegin() {
+  return layer_list_.rbegin();
 }
 
-LayerListReverseIterator<LayerImpl> LayerTreeImpl::rend() {
-  return LayerListReverseIterator<LayerImpl>(nullptr);
+std::vector<LayerImpl*>::reverse_iterator LayerTreeImpl::rend() {
+  return layer_list_.rend();
 }
 
 void LayerTreeImpl::AddToElementMap(LayerImpl* layer) {