Add a flag to filter out high-cost networks.

webrtc/p2p/base/portallocator.h

Index: webrtc/p2p/base/portallocator.h
diff --git a/webrtc/p2p/base/portallocator.h b/webrtc/p2p/base/portallocator.h
index 879657081a5372f1248178964523c0d5ed2d1539..dcb39168f19d06465aa505ada588a4d61a3f5d81 100644
--- a/webrtc/p2p/base/portallocator.h
+++ b/webrtc/p2p/base/portallocator.h
@@ -61,6 +61,16 @@ enum {
   // Disallow use of UDP when connecting to a relay server. Since proxy servers
   // usually don't handle UDP, using UDP will leak the IP address.
   PORTALLOCATOR_DISABLE_UDP_RELAY = 0x1000,
+
+  // When multiple networks exist, gather candidates only on the one with
+  // the lowest cost. So if both Wifi and Cellular networks exist, gather

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

Cellular => cellular 
Wifi => wifi (or Wi-Fi)

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

Done.

+  // only on the Wifi network. If a network type is "unknown", it has a cost
+  // lower than Cellular but higher than Wifi/Ethernet. So if an unknown network
+  // exists, Cellular networks will not be gathered on and if a Wifi network is

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

gathered on => gathered on it

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

Revised this.

+  // present, "unknown" networks will not be gathered on. Doing so ensures that

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

networks will not be gathered on => networks will not be used for gathering

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

Done.

+  // even if a cellular network type was not detected initially, it would not be
+  // gathered on if a Wifi network is present.
+  PORTALLOCATOR_GATHER_LOW_COST_NETWORK_ONLY = 0x2000,

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

Following the existing naming scheme, would this be
PORTALLOCATOR_DISABLE_COSTLY_NETWORKS?

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

Done.

 };
 
 const uint32_t kDefaultPortAllocatorFlags = 0;