Move surface reference code to CompositorFrameSinkSupport.

cc/surfaces/referenced_surface_tracker.h

 // Copyright 2016 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_REFERENCED_SURFACE_TRACKER_H_
 #define CC_SURFACES_REFERENCED_SURFACE_TRACKER_H_
 
 #include <unordered_set>
 #include <vector>
 
 #include "base/macros.h"
 #include "cc/surfaces/frame_sink_id.h"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surface_reference.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace cc {
 
 // Tracks surface references for a client surface. UpdateReferences() should be
 // called once per CompositorFrame to populate |references_to_add_| and
 // |references_to_remove_|.
 class CC_SURFACES_EXPORT ReferencedSurfaceTracker {
  public:
   explicit ReferencedSurfaceTracker(const FrameSinkId& frame_sink_id);
   ~ReferencedSurfaceTracker();
 
   const SurfaceId& current_surface_id() const { return current_surface_id_; }
 
-  std::vector<SurfaceReference>& references_to_add() {
+  const std::vector<SurfaceReference>& references_to_add() const {
     return references_to_add_;
   }
 
-  std::vector<SurfaceReference>& references_to_remove() {
+  const std::vector<SurfaceReference>& references_to_remove() const {
     return references_to_remove_;
   }
 
   // Update the references for a CompositorFrame. If |local_surface_id| has
   // changed then new references will be generated for everything in
   // |referenced_surfaces|. Otherwise a diff from the referenced surfaces in the
   // last frame will be computed. This should be called once per
   // CompositorFrame.
   void UpdateReferences(const LocalSurfaceId& local_surface_id,
                         const std::vector<SurfaceId>& referenced_surfaces);
@@ skipping 25 matching lines @@
   // CompositorFrame has been submitted and the surfaces are no longer needed by
   // |current_surface_id_|.
   std::vector<SurfaceReference> references_to_remove_;
 
   DISALLOW_COPY_AND_ASSIGN(ReferencedSurfaceTracker);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_REFERENCED_SURFACE_TRACKER_H_