Add network cost as part of the connection comparison.

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 ac7acabf057cdd06fa4beb915989bc49d65f04ec..a4335f838b51a024e08828dc6f87761319595ab5 100644
--- a/webrtc/p2p/base/candidate.h
+++ b/webrtc/p2p/base/candidate.h
@@ -27,6 +27,8 @@
 
 namespace cricket {
 
+const uint32_t kMaxNetworkCost = 0xFFFF;

[pthatcher1, 2016/02/12 00:07:12]

Can we make it something that is going to look reasonable in the SDP/signalling?
 LIke, 1,000?  That would be equivalent to a 10 second RTT with 10ms resolution,
which sounds like a reasonable max, and would look good in the signalling. 
Plus, it would leave us plenty of head room for things in the future.

[honghaiz3, 2016/02/12 19:28:43]

Changed to 999. (digit 9 is a better convention to be the maximum number for
human being (or maybe just me)).

[pthatcher1, 2016/02/12 20:05:26]

Sounds good.

+
 // Candidate for ICE based connection discovery.
 
 class Candidate {
@@ -138,6 +140,15 @@ class Candidate {
     ist >> generation_;
   }
 
+  // |network_cost| measures the cost/penalty of using this candidate. A network
+  // cost of 0 indicates this candidate can be used freely. A value of
+  // |kMaxNetworkCost| indicates it should be used only as the last resort.
+  void set_network_cost(uint32_t network_cost) {
+    ASSERT(network_cost <= kMaxNetworkCost);
+    network_cost_ = network_cost;
+  }
+  uint32_t network_cost() const { return network_cost_; }
+
   const std::string& foundation() const {
     return foundation_;
   }
@@ -211,10 +222,10 @@ class Candidate {
     std::ostringstream ost;
     std::string address = sensitive ? address_.ToSensitiveString() :
                                       address_.ToString();
-    ost << "Cand[" << foundation_ << ":" << component_ << ":"
-        << protocol_ << ":" << priority_ << ":"
-        << address << ":" << type_ << ":" << related_address_ << ":"
-        << username_ << ":" << password_ << "]";
+    ost << "Cand[" << foundation_ << ":" << component_ << ":" << protocol_
+        << ":" << priority_ << ":" << address << ":" << type_ << ":"
+        << related_address_ << ":" << username_ << ":" << password_ << ":"
+        << network_cost_ << "]";
     return ost.str();
   }
 
@@ -233,6 +244,7 @@ class Candidate {
   std::string foundation_;
   rtc::SocketAddress related_address_;
   std::string tcptype_;
+  uint32_t network_cost_ = 0;
 };
 
 // Used during parsing and writing to map component to channel name