Add cc::Surface ref counting.

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 9ba2eea2543043d8f7d06e6a5c9738185924b25d..5db5f15cd0504b0dccdc17637db1c1ec8f500163 100644
--- a/cc/surfaces/surface_manager.h
+++ b/cc/surfaces/surface_manager.h
@@ -30,6 +30,8 @@ class SurfaceFactoryClient;
 
 class CC_SURFACES_EXPORT SurfaceManager {
  public:
+  using SurfaceIdSet = std::unordered_set<SurfaceId, SurfaceIdHash>;
+
   SurfaceManager();
   ~SurfaceManager();
 
@@ -66,6 +68,32 @@ class CC_SURFACES_EXPORT SurfaceManager {
   // possibly because a renderer process has crashed.
   void InvalidateFrameSinkId(const FrameSinkId& frame_sink_id);
 
+  // Adds a reference from a parent surface to a child surface. This signifies
+  // the parent surface is embedding the child surface and the child surface
+  // is needed until the reference is removed.
+  void AddSurfaceIdReference(const SurfaceId& parent_id,
+                             const SurfaceId& child_id);
+
+  // Removes a reference from a parent surface to a child surface. This signals
+  // the parent surface no longer needs the child surface. Will run GC if
+  // |should_run_gc| is true and child surface drops to zero references.
+  void RemoveSurfaceIdReference(const SurfaceId& parent_id,
+                                const SurfaceId& child_id,
+                                bool should_run_gc = true);
+
+  // Removes all references to and from surfaces that were created for
+  // |frame_sink_id|.
+  void RemoveAllReferencesForFrameSink(const FrameSinkId& frame_sink_id);
+  void RemoveAllReferencesForSurfaceId(const SurfaceId& surface_id);
+
+  // Returns the number of surfaces that have references to |surface_id|. When
+  // the count is zero nothing is referencing the surface and it may be garbage
+  // collected.
+  size_t GetSurfaceReferenceCount(const SurfaceId& surface_id) const;
+
+  // Returns the number of surfaces that |surface_id| refers to.
+  size_t GetSurfaceRefereeCount(const SurfaceId& surface_id) const;
+
   // SurfaceFactoryClient, hierarchy, and BeginFrameSource can be registered
   // and unregistered in any order with respect to each other.
   //
@@ -147,6 +175,16 @@ class CC_SURFACES_EXPORT SurfaceManager {
   };
   std::unordered_map<FrameSinkId, FrameSinkSourceMapping, FrameSinkIdHash>
       frame_sink_source_map_;
+
+  // References from the child surface to parent surface. If there are zero
+  // entries in the set for a SurfaceId then nothing is referencing the surface
+  // and it can be garbage collected.
+  std::unordered_map<SurfaceId, SurfaceIdSet, SurfaceIdHash>
+      child_to_parent_refs_;
+  // References from the parent surface to child surface.
+  std::unordered_map<SurfaceId, SurfaceIdSet, SurfaceIdHash>
+      parent_to_child_refs_;
+
   // Set of which sources are registered to which namespace.  Any child
   // that is implicitly using this namespace must be reachable by the
   // parent in the dag.