Refactor gpu::Buffer to allow different types of backing

gpu/command_buffer/common/buffer.h

 // Copyright (c) 2014 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 GPU_COMMAND_BUFFER_COMMON_BUFFER_H_
 #define GPU_COMMAND_BUFFER_COMMON_BUFFER_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
 #include "gpu/command_buffer/common/types.h"
 #include "gpu/gpu_export.h"
 
 namespace base {
   class SharedMemory;
 }
 
 namespace gpu {
 
+class GPU_EXPORT BufferBacking {
+ public:
+  virtual ~BufferBacking() {}
+  virtual void* GetMemory() const = 0;
+  virtual size_t GetSize() const = 0;
+};
+
+class GPU_EXPORT SharedMemoryBufferBacking : public BufferBacking {
+ public:
+  SharedMemoryBufferBacking(scoped_ptr<base::SharedMemory> shared_memory,
+                            size_t size);
+  virtual ~SharedMemoryBufferBacking();
+  virtual void* GetMemory() const OVERRIDE;
+  virtual size_t GetSize() const OVERRIDE;
+  base::SharedMemory* shared_memory() { return shared_memory_.get(); }
+
+ private:
+  scoped_ptr<base::SharedMemory> shared_memory_;
+  size_t size_;
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryBufferBacking);
+};
+
 // Buffer owns a piece of shared-memory of a certain size.
 class GPU_EXPORT Buffer : public base::RefCountedThreadSafe<Buffer> {
  public:
-  Buffer(scoped_ptr<base::SharedMemory> shared_memory, size_t size);
+  explicit Buffer(scoped_ptr<BufferBacking> backing);
 
-  base::SharedMemory* shared_memory() const { return shared_memory_.get(); }
+  BufferBacking* backing() const { return backing_.get(); }
   void* memory() const { return memory_; }
   size_t size() const { return size_; }
 
   // Returns NULL if the address overflows the memory.
   void* GetDataAddress(uint32 data_offset, uint32 data_size) const;
 
  private:
   friend class base::RefCountedThreadSafe<Buffer>;
   ~Buffer();
 
-  scoped_ptr<base::SharedMemory> shared_memory_;
+  scoped_ptr<BufferBacking> backing_;
   void* memory_;
   size_t size_;
 
   DISALLOW_COPY_AND_ASSIGN(Buffer);
 };
 
+static inline scoped_ptr<BufferBacking> MakeBackingFromSharedMemory(
+    scoped_ptr<base::SharedMemory> shared_memory,
+    size_t size) {
+  return scoped_ptr<BufferBacking>(
+      new SharedMemoryBufferBacking(shared_memory.Pass(), size));
+}
+
+static inline scoped_refptr<Buffer> MakeBufferFromSharedMemory(
+    scoped_ptr<base::SharedMemory> shared_memory,
+    size_t size) {
+  return new Buffer(MakeBackingFromSharedMemory(shared_memory.Pass(), size));
+}
+
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_BUFFER_H_