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

cc/layers/layer_impl.h

 // Copyright 2011 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_LAYER_IMPL_H_
 #define CC_LAYERS_LAYER_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 413 matching lines @@
   bool TransformAnimationBoundsForBox(const gfx::BoxF& box,
                                       gfx::BoxF* bounds) const;
 
   // Note this rect is in layer space (not content space).
   void SetUpdateRect(const gfx::Rect& update_rect);
   const gfx::Rect& update_rect() const { return update_rect_; }
 
   void AddDamageRect(const gfx::Rect& damage_rect);
   const gfx::Rect& damage_rect() const { return damage_rect_; }
 
-  virtual base::DictionaryValue* LayerTreeAsJson() const;
+  virtual std::unique_ptr<base::DictionaryValue> LayerTreeAsJson() const;
 
   bool LayerPropertyChanged() const;
 
   void ResetChangeTracking();
 
   virtual SimpleEnclosedRegion VisibleOpaqueRegion() const;
 
   virtual void DidBecomeActive() {}
 
   virtual void DidBeginTracing();
@@ skipping 208 matching lines @@
 
   bool scrolls_drawn_descendant_;
   bool has_will_change_transform_hint_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_