cc: Make LayerTreeImpl dump layer list to FrameViewer and Devtools

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index d80db11a5f2329ced181089b7fa787930dd5122a..96c5e06c8af0de5038ad04ba3e64b145fd46f270 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -160,6 +160,8 @@ class CC_EXPORT LayerTreeImpl {
 
   LayerListIterator<LayerImpl> begin();
   LayerListIterator<LayerImpl> end();
+  LayerListIterator<LayerImpl> begin() const;

[vmpstr, 2016/05/31 22:16:16]

You should either have LayerListIterator<const LayerImpl> here or just add const
qualifier to the existing begin/end functions. I don't think you're buying much
with non-const if you have const ones that return the same type. Wdyt?

+  LayerListIterator<LayerImpl> end() const;
   LayerListReverseIterator<LayerImpl> rbegin();
   LayerListReverseIterator<LayerImpl> rend();