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

cc/layers/ui_resource_layer_impl.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYERS_UI_RESOURCE_LAYER_IMPL_H_
 #define CC_LAYERS_UI_RESOURCE_LAYER_IMPL_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 31 matching lines @@
   void SetVertexOpacity(const float vertex_opacity[4]);
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
   void PushPropertiesTo(LayerImpl* layer) override;
 
   bool WillDraw(DrawMode draw_mode,
                 ResourceProvider* resource_provider) override;
   void AppendQuads(RenderPass* render_pass,
                    AppendQuadsData* append_quads_data) override;
 
-  base::DictionaryValue* LayerTreeAsJson() const override;
+  std::unique_ptr<base::DictionaryValue> LayerTreeAsJson() const override;
 
  protected:
   UIResourceLayerImpl(LayerTreeImpl* tree_impl, int id);
 
   // The size of the resource bitmap in pixels.
   gfx::Size image_bounds_;
 
   UIResourceId ui_resource_id_;
 
   gfx::PointF uv_top_left_;
   gfx::PointF uv_bottom_right_;
   float vertex_opacity_[4];
 
  private:
   const char* LayerTypeAsString() const override;
 
   DISALLOW_COPY_AND_ASSIGN(UIResourceLayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_UI_RESOURCE_LAYER_IMPL_H_