Change LayerImpl::LayerTreeAsJson to return a std::unique_ptr.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 8ad4c011597ac57e884a3f883e8d4b2f553c638b..d1cf729d6265bfc57d9950935f1e925286eb1991 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -497,8 +497,8 @@ gfx::Vector2dF LayerImpl::FixedContainerSizeDelta() const {
   return scroll_clip_layer->bounds_delta();
 }
 
-base::DictionaryValue* LayerImpl::LayerTreeAsJson() const {
-  base::DictionaryValue* result = new base::DictionaryValue;
+std::unique_ptr<base::DictionaryValue> LayerImpl::LayerTreeAsJson() const {
+  std::unique_ptr<base::DictionaryValue> result(new base::DictionaryValue);
   result->SetInteger("LayerId", id());
   result->SetString("LayerType", LayerTypeAsString());