Fix some warnings in ObjC code.

webrtc/api/objc/RTCDataChannel.h

 /*
  *  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 28 matching lines @@
 - (void)dataChannelDidChangeState:(RTCDataChannel *)dataChannel;
 
 /** The data channel successfully received a data buffer. */
 - (void)dataChannel:(RTCDataChannel *)dataChannel
     didReceiveMessageWithBuffer:(RTCDataBuffer *)buffer;
 
 @optional
 
 /** The data channel's |bufferedAmount| changed. */
 - (void)dataChannel:(RTCDataChannel *)dataChannel
-    didChangeBufferedAmount:(NSUInteger)amount;
+    didChangeBufferedAmount:(uint64_t)amount;
 
 @end
 
 
 /** Represents the state of the data channel. */
 typedef NS_ENUM(NSInteger, RTCDataChannelState) {
     RTCDataChannelStateConnecting,
     RTCDataChannelStateOpen,
     RTCDataChannelStateClosing,
     RTCDataChannelStateClosed,
@@ skipping 51 matching lines @@
 
 /** Closes the data channel. */
 - (void)close;
 
 /** Attempt to send |data| on this data channel's underlying data transport. */
 - (BOOL)sendData:(RTCDataBuffer *)data;
 
 @end
 
 NS_ASSUME_NONNULL_END