Add/remove surface references via MojoCompositorFrameSink.

cc/surfaces/surface_manager.h

Index: cc/surfaces/surface_manager.h
diff --git a/cc/surfaces/surface_manager.h b/cc/surfaces/surface_manager.h
index 9e6144bf6879252c5b53fe90f5fdbf4c872a39bc..190c722bea5c393cd451ef320168092367074c44 100644
--- a/cc/surfaces/surface_manager.h
+++ b/cc/surfaces/surface_manager.h
@@ -103,6 +103,8 @@ class CC_SURFACES_EXPORT SurfaceManager
   void UnregisterFrameSinkHierarchy(const FrameSinkId& parent_frame_sink_id,
                                     const FrameSinkId& child_frame_sink_id);
 
+  void PrintReferenceTree(const std::string& name);
+
   // SurfaceReferenceManager:
   const SurfaceId& GetRootSurfaceId() const override;
   void AddSurfaceReference(const SurfaceId& parent_id,
@@ -113,6 +115,10 @@ class CC_SURFACES_EXPORT SurfaceManager
   size_t GetReferencedSurfaceCount(const SurfaceId& surface_id) const override;
 
  private:
+  void PrintReferenceTreeImpl(const SurfaceId& surface_id,
+                              std::string indent,
+                              std::string* str);
+
   void RecursivelyAttachBeginFrameSource(const FrameSinkId& frame_sink_id,
                                          BeginFrameSource* source);
   void RecursivelyDetachBeginFrameSource(const FrameSinkId& frame_sink_id,
@@ -183,7 +189,7 @@ class CC_SURFACES_EXPORT SurfaceManager
 
   // Root SurfaceId that references display root surfaces. There is no Surface
   // with this id, it's for bookkeeping purposes only.
-  const SurfaceId kRootSurfaceId;
+  const SurfaceId root_surface_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceManager);
 };