Fill the remote pwd in ice candidates when an ICE credential is received.

webrtc/p2p/base/candidate.h

Index: webrtc/p2p/base/candidate.h
diff --git a/webrtc/p2p/base/candidate.h b/webrtc/p2p/base/candidate.h
index 3f0ea43cde21fd9239ceb48d65bdaa9b5fc1b8bf..ac7acabf057cdd06fa4beb915989bc49d65f04ec 100644
--- a/webrtc/p2p/base/candidate.h
+++ b/webrtc/p2p/base/candidate.h
@@ -105,6 +105,7 @@ class Candidate {
         std::min(prio_val, static_cast<uint64_t>(UINT_MAX)));
   }
 
+  // TODO(honghaiz): Change to usernameFragment or ufrag.
   const std::string & username() const { return username_; }
   void set_username(const std::string & username) { username_ = username; }