clang/win: Fix -Wextra warnings in webrtc.

webrtc/base/sec_buffer.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 101 matching lines @@
   ~CSecBufferBundle() {
     Release();
   }
 
   // Accessor for the descriptor
   PSecBufferDesc desc() {
     return &desc_;
   }
 
   // Accessor for the descriptor
-  const PSecBufferDesc desc() const {
+  PSecBufferDesc desc() const {
     return &desc_;
   }
 
   // returns the i-th security buffer
   SecBuffer &operator[] (size_t num) {
     ASSERT(num < num_buffers); // "Buffer index out of bounds"
     return buffers_[num];
   }
 
   // returns the i-th security buffer
@@ skipping 14 matching lines @@
   // Our descriptor
   SecBufferDesc               desc_;
   // Our bundled buffers, each takes care of its own
   // initialization and destruction
   CSecBuffer<pfnFreeBuffer>   buffers_[num_buffers];
 };
 
 } // namespace rtc
 
 #endif  // WEBRTC_BASE_SEC_BUFFER_H__