Create the SrtpTransportInterface.

webrtc/api/ortc/srtptransportinterface.h

+/*
+ *  Copyright 2017 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.
+ */
+
+#ifndef WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_
+#define WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_
+
+#include "webrtc/api/ortc/rtptransportinterface.h"
+#include "webrtc/api/rtcerror.h"
+#include "webrtc/media/base/cryptoparams.h"
+
+namespace webrtc {
+
+// The subclass of the RtpTransport which uses the SRTP. The Keying information

[Taylor Brandstetter, 2017/02/24 18:57:57]

nit: Don't need "the" before "SRTP"

[Zhi Huang, 2017/02/27 05:16:00]

Done.

+// is explicitly passed in from the application.

[Taylor Brandstetter, 2017/02/24 18:57:57]

May also want to note that this is similar in role to Edge's RTCSrtpSdesTranport
(https://msdn.microsoft.com/en-us/library/mt502527(v=vs.85).aspx). And describe
how it could be used to implement SDES. Namely, after applying an answer, the
negotiated keying information in the offer and answer would be set.

[Zhi Huang, 2017/02/27 05:16:00]

Done.

+class SrtpTransportInterface : public RtpTransportInterface {
+ public:
+  virtual ~SrtpTransportInterface() {}
+
+  // Set the SRTP keying material for sending stream from the applciation.

[Taylor Brandstetter, 2017/02/24 18:57:57]

nit: "application" misspelled. 

It may also be better to use the phrases "outgoing RTP streams" and "incoming
RTP streams" instead of "sending stream" and "receiving stream".

[Zhi Huang, 2017/02/27 05:16:00]

Done.

+  virtual RTCError SetSrtpSendKey(const cricket::CryptoParams& params) = 0;
+
+  // Set the SRTP keying material for receiving stream from the application.
+  virtual RTCError SetSrtpReceiveKey(const cricket::CryptoParams& params) = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_