Added LayerTreeHostImpl::layerTreeAsJson which serializes a layer tree

cc/layer_impl.h

Index: cc/layer_impl.h
diff --git a/cc/layer_impl.h b/cc/layer_impl.h
index 76a3e38daf3bdd7904a73259bb210c356d077ce7..26e476bb349649dba556ad5a8c5e543921a9c64e 100644
--- a/cc/layer_impl.h
+++ b/cc/layer_impl.h
@@ -27,6 +27,10 @@
 #include "ui/gfx/rect_f.h"
 #include "ui/gfx/transform.h"
 
+namespace base {
+class DictionaryValue;
+}
+
 namespace cc {
 
 class LayerTreeHostImpl;
@@ -242,6 +246,7 @@ public:
     void setUpdateRect(const gfx::RectF& updateRect) { m_updateRect = updateRect; }
 
     std::string layerTreeAsText() const;
+    virtual base::DictionaryValue* layerTreeAsJson() const;
 
     void setStackingOrderChanged(bool);