Add a flag to filter out high-cost networks.

webrtc/p2p/client/basicportallocator.cc

Index: webrtc/p2p/client/basicportallocator.cc
diff --git a/webrtc/p2p/client/basicportallocator.cc b/webrtc/p2p/client/basicportallocator.cc
index 143b036183777875730387f85736ed71ad90e3db..141ee9aa5dcc565d6d7c6cea5a69e90a80b96227 100644
--- a/webrtc/p2p/client/basicportallocator.cc
+++ b/webrtc/p2p/client/basicportallocator.cc
@@ -393,6 +393,21 @@ void BasicPortAllocatorSession::GetNetworks(
                                           network->type();
                                  }),
                   networks->end());
+
+  if (flags() & PORTALLOCATOR_GATHER_LOW_COST_NETWORK_ONLY) {
+    uint16_t lowest_cost = rtc::kMaxNetworkCost;
+    for (rtc::Network* network : *networks) {
+      uint16_t cost = network->GetCost();
+      if (cost < lowest_cost) {
+        lowest_cost = cost;
+      }
+    }

[pthatcher1, 2016/05/17 20:44:28]

std::min might work here

[honghaiz3, 2016/05/18 05:55:02]

Done.

+    networks->erase(std::remove_if(networks->begin(), networks->end(),
+                                   [lowest_cost](rtc::Network* network) {
+                                     return network->GetCost() > lowest_cost;
+                                   }),
+                    networks->end());

[pthatcher1, 2016/05/17 20:44:28]

We could use a threshold greater than zero (perhaps 50), such as "return
network->GetCost() > lowest_cost + kNetworkCostLow"

[honghaiz3, 2016/05/18 05:55:02]

Done.

+  }
 }
 
 // For each network, see if we have a sequence that covers it already.  If not,