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

cc/surfaces/frame_sink_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_FRAME_SINK_MANAGER_H_
 #define CC_SURFACES_FRAME_SINK_MANAGER_H_
 
 #include <stdint.h>
 
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "cc/surfaces/frame_sink_id.h"
+#include "cc/surfaces/primary_begin_frame_source.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace cc {
 class BeginFrameSource;
 class FrameSinkManagerClient;
 
 namespace test {
 class SurfaceSynchronizationTest;
 }
 
@@ skipping 23 matching lines @@
                                       FrameSinkManagerClient* client);
   void UnregisterFrameSinkManagerClient(const FrameSinkId& frame_sink_id);
 
   // Associates a |source| with a particular framesink.  That framesink and
   // any children of that framesink with valid clients can potentially use
   // that |source|.
   void RegisterBeginFrameSource(BeginFrameSource* source,
                                 const FrameSinkId& frame_sink_id);
   void UnregisterBeginFrameSource(BeginFrameSource* source);
 
+  // Returns a stable BeginFrameSource that forwards BeginFrames from the first
+  // available BeginFrameSource.
+  BeginFrameSource* GetPrimaryBeginFrameSource();
+
   // Register a relationship between two framesinks.  This relationship means
   // that surfaces from the child framesik will be displayed in the parent.
   // Children are allowed to use any begin frame source that their parent can
   // use.
   void RegisterFrameSinkHierarchy(const FrameSinkId& parent_frame_sink_id,
                                   const FrameSinkId& child_frame_sink_id);
   void UnregisterFrameSinkHierarchy(const FrameSinkId& parent_frame_sink_id,
                                     const FrameSinkId& child_frame_sink_id);
 
   // Export list of valid frame_sink_ids for SatisfyDestructionDeps in surface
@@ skipping 22 matching lines @@
 
   // Begin frame source routing. Both BeginFrameSource and
   // CompositorFrameSinkSupport pointers guaranteed alive by callers until
   // unregistered.
   struct FrameSinkSourceMapping {
     FrameSinkSourceMapping();
     FrameSinkSourceMapping(const FrameSinkSourceMapping& other);
     ~FrameSinkSourceMapping();
     bool has_children() const { return !children.empty(); }
     // The currently assigned begin frame source for this client.
-    BeginFrameSource* source;
+    BeginFrameSource* source = nullptr;
     // This represents a dag of parent -> children mapping.
     std::vector<FrameSinkId> children;
   };
 
   std::unordered_map<FrameSinkId, FrameSinkManagerClient*, FrameSinkIdHash>
       clients_;
 
   std::unordered_map<FrameSinkId, FrameSinkSourceMapping, FrameSinkIdHash>
       frame_sink_source_map_;
 
-  // Set of which sources are registered to which frmesinks.  Any child
+  // Set of BeginFrameSource along with associated FrameSinkIds. Any child
   // that is implicitly using this framesink must be reachable by the
   // parent in the dag.
   std::unordered_map<BeginFrameSource*, FrameSinkId> registered_sources_;
 
+  PrimaryBeginFrameSource primary_source_;
+
   DISALLOW_COPY_AND_ASSIGN(FrameSinkManager);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_FRAME_SINK_MANAGER_H_