Mozart: Improve internal scene graph representation.

services/gfx/compositor/compositor_engine.h

 // Copyright 2015 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 SERVICES_GFX_COMPOSITOR_COMPOSITOR_H_
 #define SERVICES_GFX_COMPOSITOR_COMPOSITOR_H_
 
 #include <unordered_map>
 #include <vector>
 
@@ skipping 87 matching lines @@
   void OnOutputError(const base::WeakPtr<RendererState>& renderer_state_weak);
   void OnOutputUpdateRequest(
       const base::WeakPtr<RendererState>& renderer_state_weak,
       const mojo::gfx::composition::FrameInfo& frame_info);
   void OnOutputSnapshotRequest(
       const base::WeakPtr<RendererState>& renderer_state_weak,
       const mojo::gfx::composition::FrameInfo& frame_info);
   void OnPresentScene(const base::WeakPtr<SceneState>& scene_state_weak,
                       int64_t presentation_time);
 
-  SceneDef* ResolveSceneReference(
-      mojo::gfx::composition::SceneToken* scene_token);
+  base::WeakPtr<SceneDef> ResolveSceneReference(
+      const mojo::gfx::composition::SceneToken& scene_token);
   void SendResourceUnavailable(SceneState* scene_state, uint32_t resource_id);
 
   SceneState* FindScene(uint32_t scene_token);
 
   bool IsSceneStateRegisteredDebug(SceneState* scene_state) {
     return scene_state && FindScene(scene_state->scene_token()->value);
   }
   bool IsRendererStateRegisteredDebug(RendererState* renderer_state) {
     return renderer_state &&
            std::any_of(renderers_.begin(), renderers_.end(),
                        [renderer_state](RendererState* other) {
                          return renderer_state == other;
                        });
   }
 
   uint32_t next_scene_token_value_ = 1u;
   uint32_t next_renderer_id_ = 1u;
   std::unordered_map<uint32_t, SceneState*> scenes_by_token_;
   std::vector<RendererState*> renderers_;
 
   base::WeakPtrFactory<CompositorEngine> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorEngine);
 };
 
 }  // namespace compositor
 
 #endif  // SERVICES_GFX_COMPOSITOR_COMPOSITOR_H_