message: Change DatagramTransportInterface methods to pure virtual.
  These methods are implemented everywhere, and no longer need to provide
  default implementations.
  Cr-Commit-Position: refs/heads/master@{#29263}
diff: @@ -58,11 +58,10 @@ class DatagramSinkInterface {
  virtual void OnDatagramSent(DatagramId datagram_id) = 0;
  // Called when datagram is ACKed.
  - // TODO(sukhanov): Make pure virtual.
  - virtual void OnDatagramAcked(const DatagramAck& datagram_ack) {}
  + virtual void OnDatagramAcked(const DatagramAck& datagram_ack) = 0;
  // Called when a datagram is lost.
  - virtual void OnDatagramLost(DatagramId datagram_id) {}
  + virtual void OnDatagramLost(DatagramId datagram_id) = 0;
  };
  // Datagram transport allows to send and receive unreliable packets (datagrams)
  @@ -140,9 +139,7 @@ class DatagramTransportInterface : public DataChannelTransportInterface {
  // For clients, the parameters echo the server configuration used to create
  // the client, possibly removing any fields or parameters which the client
  // does not understand.
  - //
  - // TODO(mellem): Make pure virtual.
  - virtual std::string GetTransportParameters() const { return ""; }
  + virtual std::string GetTransportParameters() const = 0;
  };
  } // namespace webrtc
  