Make mojo::internal::Buffer a non-virtual class.

mojo/public/cpp/bindings/lib/message_buffer.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 MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_LIB_MESSAGE_BUFFER_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_LIB_MESSAGE_BUFFER_H_
 
-#include <stddef.h>
 #include <stdint.h>
 
 #include <utility>
 
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/lib/buffer.h"
 #include "mojo/public/cpp/system/message.h"
 
 namespace mojo {
 namespace internal {
 
-// A fixed-size Buffer implementation using a Mojo message object for storage.
+// A fixed-size Buffer using a Mojo message object for storage.
 class MessageBuffer : public Buffer {
  public:
   // Initializes this buffer to carry a fixed byte capacity and no handles.
   MessageBuffer(size_t capacity, bool zero_initialized);
 
   // Initializes this buffer from an existing Mojo MessageHandle.
   MessageBuffer(ScopedMessageHandle message, uint32_t num_bytes);
 
-  ~MessageBuffer() override;
-
-  void* data() const { return buffer_; }
-  uint32_t data_num_bytes() const { return data_num_bytes_; }
-
-  // Buffer:
-  void* Allocate(size_t delta) override;
+  ~MessageBuffer();
 
   ScopedMessageHandle TakeMessage() { return std::move(message_); }
 
   void NotifyBadMessage(const std::string& error);
 
  private:
-  uint32_t data_num_bytes_ = 0;
   ScopedMessageHandle message_;
-  void* buffer_;
-
-  uint32_t bytes_claimed_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(MessageBuffer);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_LIB_MESSAGE_BUFFER_H_