Let receiving() and SignalReceivingState be part of rtc::PacketTransportInterface.

webrtc/p2p/base/packettransportinterface.h

 /*
  *  Copyright 2016 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 18 matching lines @@
 class PacketTransportInterface : public sigslot::has_slots<> {
  public:
   virtual ~PacketTransportInterface() {}
 
   // Identify the object for logging and debug purpose.
   virtual const std::string debug_name() const = 0;
 
   // The transport has been established.
   virtual bool writable() const = 0;
 
+  // The transport has received at least one packet.

[pthatcher1, 2016/10/31 18:27:30]

That's not what receiving() means.  It means that the transport has received a
packet in the last X milliseconds, where X is typically settable.  But I'm OK
with this CL without it being settable.  Perhaps update the comment to be "The
transport has received a packet in the last X milliseconds, here X is configured
by each implementation."

[johan, 2016/10/31 19:03:31]

Ok, I missed the periodic check in Connection::UpdateState /
Connection::UpdateReceiving.
Comment updated.

+  virtual bool receiving() const = 0;
+
   // Attempts to send the given packet.
   // The return value is < 0 on failure. The return value in failure case is not
   // descriptive. Depending on failure cause and implementation details
   // GetError() returns an descriptive errno.h error value.
   // This mimics posix socket send() or sendto() behavior.
   // TODO(johan): Reliable, meaningful, consistent error codes for all
   // implementations would be nice.
   // TODO(johan): Remove the default argument once channel code is updated.
   virtual int SendPacket(const char* data,
                          size_t len,
@@ skipping 14 matching lines @@
   // Emitted when the writable state, represented by |writable()|, changes.
   sigslot::signal1<PacketTransportInterface*> SignalWritableState;
 
   //  Emitted when the PacketTransportInterface is ready to send packets. "Ready
   //  to send" is more sensitive than the writable state; a transport may be
   //  writable, but temporarily not able to send packets. For example, the
   //  underlying transport's socket buffer may be full, as indicated by
   //  SendPacket's return code and/or GetError.
   sigslot::signal1<PacketTransportInterface*> SignalReadyToSend;
 
+  // Emitted when receiving state changes to true.
+  sigslot::signal1<PacketTransportInterface*> SignalReceivingState;
+
   // Signalled each time a packet is received on this channel.
   sigslot::signal5<PacketTransportInterface*,
                    const char*,
                    size_t,
                    const rtc::PacketTime&,
                    int>
       SignalReadPacket;
 
   // Signalled each time a packet is sent on this channel.
   sigslot::signal2<PacketTransportInterface*, const rtc::SentPacket&>
       SignalSentPacket;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_