Replacing SurfaceReferenceBase and SequenceSurfaceReference with Closures

cc/surfaces/surface_reference_factory.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_SURFACE_REFERENCE_FACTORY_H_
 #define CC_SURFACES_SURFACE_REFERENCE_FACTORY_H_
 
+#include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surface_reference_owner.h"
 
 namespace cc {
 
-class SurfaceReferenceBase;
-
-// Creates surface references. Returns an object of type
-// SurfaceReferenceBase which holds on to its corresponding
-// surface reference until destruction. The referenced surface
-// will be kept alive as long as there is a reference to it.
+// Creates surface references. The referenced surface will be kept alive as
+// long as there is a reference to it.
 class SurfaceReferenceFactory
     : public base::RefCountedThreadSafe<SurfaceReferenceFactory> {
  public:
-  virtual std::unique_ptr<SurfaceReferenceBase> CreateReference(
-      SurfaceReferenceOwner* owner,
-      const SurfaceId& surface_id) const = 0;
+  // Creates a reference to the surface with the given surface id and returns
+  // a closure that must be called exactly once to remove the reference.
+  virtual base::Closure CreateReference(SurfaceReferenceOwner* owner,
+                                        const SurfaceId& surface_id) const = 0;
 
   SurfaceReferenceFactory() = default;
 
  protected:
   virtual ~SurfaceReferenceFactory() = default;
 
  private:
-  friend class SurfaceReferenceBase;
   friend class base::RefCountedThreadSafe<SurfaceReferenceFactory>;
 
-  virtual void DestroyReference(SurfaceReferenceBase* surface_ref) const = 0;
-
   DISALLOW_COPY_AND_ASSIGN(SurfaceReferenceFactory);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_REFERENCE_FACTORY_H_