Reland Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/api/objc/RTCDataChannel.mm

 /*
  *  Copyright 2015 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 35 matching lines @@
 }
 
 
 @implementation RTCDataBuffer {
   rtc::scoped_ptr<webrtc::DataBuffer> _dataBuffer;
 }
 
 - (instancetype)initWithData:(NSData *)data isBinary:(BOOL)isBinary {
   NSParameterAssert(data);
   if (self = [super init]) {
-    rtc::Buffer buffer(reinterpret_cast<const uint8_t*>(data.bytes),
-                       data.length);
+    rtc::CopyOnWriteBuffer buffer(
+        reinterpret_cast<const uint8_t*>(data.bytes), data.length);
     _dataBuffer.reset(new webrtc::DataBuffer(buffer, isBinary));
   }
   return self;
 }
 
 - (NSData *)data {
   return [NSData dataWithBytes:_dataBuffer->data.data()
                         length:_dataBuffer->data.size()];
 }
 
@@ skipping 146 matching lines @@
     case RTCDataChannelStateOpen:
       return @"Open";
     case RTCDataChannelStateClosing:
       return @"Closing";
     case RTCDataChannelStateClosed:
       return @"Closed";
   }
 }
 
 @end