Implement the "needs-ice-restart" logic for SetConfiguration.

webrtc/p2p/base/jseptransport.h

Index: webrtc/p2p/base/jseptransport.h
diff --git a/webrtc/p2p/base/jseptransport.h b/webrtc/p2p/base/jseptransport.h
index 9684770bf7ad63f20f61b6f9457e9e3b3838f95f..51f75b228f9fe5a646034fde289eb46d6ccb2e25 100644
--- a/webrtc/p2p/base/jseptransport.h
+++ b/webrtc/p2p/base/jseptransport.h
@@ -288,6 +288,14 @@ class JsepTransport : public sigslot::has_slots<> {
                                      ContentAction action,
                                      std::string* error_desc);
 
+  // Set the "needs-ice-restart" flag as described in JSEP.
+  // This and the below method can be called safely from any thread as long as
+  // SetXTransportDescription is not in progress.

[pthatcher1, 2016/12/10 02:26:31]

And if SetXTransportDescription is in progress, what happens?

[Taylor Brandstetter, 2016/12/10 19:00:35]

Undefined behavior. So don't do that.

+  void SetNeedsIceRestartFlag();
+  // Returns true if the ICE restart flag above was set, and no ICE restart has
+  // occurred yet for this transport.

[pthatcher1, 2016/12/10 02:26:31]

"no ICE restart has occured", meaning that an ICE restart has been proposed (by
local or remote) or finalized (by both)?  This may not matter now, but it will
when we add rollback.

[Taylor Brandstetter, 2016/12/10 19:00:35]

I clarified the comments. As for rollback, there are tons of things we'll need
to figure out when we start supporting that. My understanding is that a rollback
reverts *all* state unless otherwise stated (such as the addTrack weirdness),
which would include the needs-ice-restart flag.

+  bool NeedsIceRestart() const;
+
   void GetSslRole(rtc::SSLRole* ssl_role) const;
 
   // TODO(deadbeef): Make this const. See comment in transportcontroller.h.
@@ -348,6 +356,8 @@ class JsepTransport : public sigslot::has_slots<> {
                                            std::string* error_desc);
 
   const std::string mid_;
+  // needs-ice-restart bit as described in JSEP.

[pthatcher1, 2016/12/10 02:26:31]

A summary of what it means would be nice, even if just one sentence.

[Taylor Brandstetter, 2016/12/10 19:00:35]

Doesn't need to be here, since this is a private variable where the comment is
just a small reminder about what it's for. But I added more comments for
SetNeedsIceRestartFlag.

+  bool needs_ice_restart_ = false;
   rtc::scoped_refptr<rtc::RTCCertificate> certificate_;
   rtc::SSLRole secure_role_ = rtc::SSL_CLIENT;
   std::unique_ptr<rtc::SSLFingerprint> remote_fingerprint_;