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

cc/layers/nine_patch_layer_impl.h

 // Copyright 2012 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_NINE_PATCH_LAYER_IMPL_H_
 #define CC_LAYERS_NINE_PATCH_LAYER_IMPL_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 48 matching lines @@
                  const gfx::Rect& border,
                  bool fill_center,
                  bool nearest_neighbor);
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
   void PushPropertiesTo(LayerImpl* layer) 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:
   NinePatchLayerImpl(LayerTreeImpl* tree_impl, int id);
 
  private:
   const char* LayerTypeAsString() const override;
 
   void CheckGeometryLimitations();
 
   // The transparent center region that shows the parent layer's contents in
   // image space.
   gfx::Rect image_aperture_;
 
   // An inset border that the patches will be mapped to.
   gfx::Rect border_;
 
   bool fill_center_;
 
   bool nearest_neighbor_;
 
   DISALLOW_COPY_AND_ASSIGN(NinePatchLayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_NINE_PATCH_LAYER_IMPL_H_