cc::SurfaceDependencyTracker should not crash when a Display goes away

cc/surfaces/surface_manager.h

 // Copyright 2014 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_SURFACES_SURFACE_MANAGER_H_
 #define CC_SURFACES_SURFACE_MANAGER_H_
 
 #include <stdint.h>
 
 #include <list>
@@ skipping 41 matching lines @@
   };
 
   explicit SurfaceManager(LifetimeType lifetime_type = LifetimeType::SEQUENCES);
   ~SurfaceManager();
 
 #if DCHECK_IS_ON()
   // Returns a string representation of all reachable surface references.
   std::string SurfaceReferencesToString();
 #endif
 
-  void SetDependencyTracker(
-      std::unique_ptr<SurfaceDependencyTracker> dependency_tracker);
-  SurfaceDependencyTracker* dependency_tracker() {
-    return dependency_tracker_.get();
-  }
+  void SetDependencyTracker(SurfaceDependencyTracker* dependency_tracker);
+  SurfaceDependencyTracker* dependency_tracker() { return dependency_tracker_; }
 
   void RequestSurfaceResolution(Surface* pending_surface);
 
+  // Creates a BeginFrameSource that tracks the first registered
+  // BeginFrameSource.
+  std::unique_ptr<BeginFrameSource> CreatePrimaryBeginFrameSource();
+
   std::unique_ptr<Surface> CreateSurface(
       base::WeakPtr<CompositorFrameSinkSupport> compositor_frame_sink_support,
       const LocalSurfaceId& local_surface_id);
 
   // Destroy the Surface once a set of sequence numbers has been satisfied.
   void DestroySurface(std::unique_ptr<Surface> surface);
 
   Surface* GetSurfaceForId(const SurfaceId& surface_id);
 
   void AddObserver(SurfaceObserver* obs) { observer_list_.AddObserver(obs); }
@@ skipping 201 matching lines @@
   // same FrameSinkId. A SurfaceId can be reconstructed with:
   //   SurfaceId surface_id(key, value[index]);
   // The LocalSurfaceIds are stored in the order the surfaces are created in. If
   // a reference is added to a later SurfaceId then all temporary references up
   // to that point will be removed. This is to handle clients getting out of
   // sync, for example the embedded client producing new SurfaceIds faster than
   // the embedding client can use them.
   std::unordered_map<FrameSinkId, std::vector<LocalSurfaceId>, FrameSinkIdHash>
       temporary_reference_ranges_;
 
-  std::unique_ptr<SurfaceDependencyTracker> dependency_tracker_;
+  SurfaceDependencyTracker* dependency_tracker_ = nullptr;
 
   base::WeakPtrFactory<SurfaceManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceManager);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_MANAGER_H_