cc: Make LayerTreeImpl dump layer list to FrameViewer and Devtools

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 6258979282addcb5664a7b0f7a6ec27376242f27..d9748375505f581b1efe2b9ca17877f5881b11a1 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -884,19 +884,11 @@ bool LayerTreeHost::UpdateLayers() {
   return result || next_commit_forces_redraw_;
 }
 
-LayerListIterator<Layer> LayerTreeHost::begin() {
+LayerListIterator<Layer> LayerTreeHost::begin() const {
   return LayerListIterator<Layer>(root_layer_.get());
 }
 
-LayerListIterator<Layer> LayerTreeHost::end() {
-  return LayerListIterator<Layer>(nullptr);
-}
-
-const LayerListIterator<Layer> LayerTreeHost::begin() const {
-  return LayerListIterator<Layer>(root_layer_.get());
-}
-
-const LayerListIterator<Layer> LayerTreeHost::end() const {
+LayerListIterator<Layer> LayerTreeHost::end() const {
   return LayerListIterator<Layer>(nullptr);
 }