Add SurfaceManager option to use references exclusively.

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 a0163579ee761b1783220b6faed22a44874a62bd..3230fb691abba75b753ad7690396bc405540dfb0 100644
--- a/cc/surfaces/surface_manager.h
+++ b/cc/surfaces/surface_manager.h
@@ -31,7 +31,13 @@ class SurfaceFactoryClient;
 
 class CC_SURFACES_EXPORT SurfaceManager : public SurfaceReferenceManager {
  public:
-  SurfaceManager();
+  enum class LifetimeType {
+    USE_REFERENCES,
+    USE_SEQUENCES,
+  };
+
+  explicit SurfaceManager(
+      LifetimeType lifetime_type = LifetimeType::USE_SEQUENCES);
   ~SurfaceManager() override;
 
   void RegisterSurface(Surface* surface);
@@ -120,6 +126,9 @@ class CC_SURFACES_EXPORT SurfaceManager : public SurfaceReferenceManager {
   bool ChildContains(const FrameSinkId& child_frame_sink_id,
                      const FrameSinkId& search_frame_sink_id) const;
 
+  // Garbage collects all destroyed surfaces not reachable from the root. Used
+  // when |use_references_| is true.
+  void GarbageCollectSurfacesFromRoot();
   void GarbageCollectSurfaces();
 
   // Removes reference from a parent surface to a child surface. Used to remove
@@ -127,6 +136,9 @@ class CC_SURFACES_EXPORT SurfaceManager : public SurfaceReferenceManager {
   void RemoveSurfaceReferenceImpl(const SurfaceId& parent_id,
                                   const SurfaceId& child_id);
 
+  // Use reference or sequence based lifetime management.
+  LifetimeType lifetime_type_;
+
   using SurfaceMap = std::unordered_map<SurfaceId, Surface*, SurfaceIdHash>;
   SurfaceMap surface_map_;
   base::ObserverList<SurfaceObserver> observer_list_;
@@ -181,7 +193,7 @@ class CC_SURFACES_EXPORT SurfaceManager : public SurfaceReferenceManager {
 
   // 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);
 };