Enable cpplint and fix cpplint errors in webrtc/api

webrtc/api/datachannelinterface.h

Index: webrtc/api/datachannelinterface.h
diff --git a/webrtc/api/datachannelinterface.h b/webrtc/api/datachannelinterface.h
index 8b788c04684a70368fa16d6fb113a3ed14e11ce8..5fa657dc53552c32aa2ddfc7d25d1a68833e12d0 100644
--- a/webrtc/api/datachannelinterface.h
+++ b/webrtc/api/datachannelinterface.h
@@ -75,7 +75,7 @@ class DataChannelObserver {
   //  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() {}