Implement out-of-process proxy for PPB_Buffer_Dev.

ppapi/cpp/dev/buffer_dev.h

 // Copyright (c) 2010 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 PPAPI_CPP_DEV_BUFFER_DEV_H_
 #define PPAPI_CPP_DEV_BUFFER_DEV_H_
 
 #include "ppapi/cpp/resource.h"
 
 namespace pp {
 
 class Instance;
 
 class Buffer_Dev : public Resource {
  public:
   // Creates an is_null() Buffer object.
   Buffer_Dev();
-
   Buffer_Dev(const Buffer_Dev& other);
 
-  // Allocates a new Buffer in the browser with the given size. The
-  // resulting object will be is_null() if the allocation failed.
+  // Creates & Maps a new Buffer in the browser with the given size. The
+  // resulting object will be is_null() if either Create() or Map() fails.
   Buffer_Dev(Instance* instance, uint32_t size);
 
+  // Unmap the underlying shared memory.
+  virtual ~Buffer_Dev();
+
   uint32_t size() const { return size_; }
   void* data() const { return data_; }
 
  private:
   void* data_;
   uint32_t size_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_BUFFER_DEV_H_
-