Enable cpplint and fix cpplint errors in webrtc/api

webrtc/api/datachannelinterface.h

 /*
  *  Copyright 2012 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 57 matching lines @@
   bool binary;
 };
 
 class DataChannelObserver {
  public:
   // The data channel state have changed.
   virtual void OnStateChange() = 0;
   //  A data buffer was successfully received.
   virtual void OnMessage(const DataBuffer& buffer) = 0;
   // The data channel's buffered_amount has changed.
-  virtual void OnBufferedAmountChange(uint64_t previous_amount){};
+  virtual void OnBufferedAmountChange(uint64_t previous_amount) {}
 
  protected:
   virtual ~DataChannelObserver() {}
 };
 
 class DataChannelInterface : public rtc::RefCountInterface {
  public:
   // Keep in sync with DataChannel.java:State and
   // RTCDataChannel.h:RTCDataChannelState.
   enum DataState {
@@ skipping 48 matching lines @@
   // Sends |data| to the remote peer.
   virtual bool Send(const DataBuffer& buffer) = 0;
 
  protected:
   virtual ~DataChannelInterface() {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_DATACHANNELINTERFACE_H_