Adding PortAllocator option to support cases where sockets can't be bound.

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 94de2b55f54fbd772fca7c776e8ba6254ede47e6..549d013a255bb54b2a42c472dcfe1d1612413c26 100644
--- a/webrtc/p2p/client/basicportallocator.cc
+++ b/webrtc/p2p/client/basicportallocator.cc
@@ -555,8 +555,9 @@ std::vector<rtc::Network*> BasicPortAllocatorSession::GetNetworks() {
     network_manager->GetNetworks(&networks);
     // If network enumeration fails, use the ANY address as a fallback, so we
     // can at least try gathering candidates using the default route chosen by
-    // the OS.
-    if (networks.empty()) {
+    // the OS. Or, if the PORTALLOCATOR_ENABLE_ANY_ADDRESS_PORTS flag is
+    // set, we'll use ANY address candidates either way.
+    if (networks.empty() || flags() & PORTALLOCATOR_ENABLE_ANY_ADDRESS_PORTS) {
       network_manager->GetAnyAddressNetworks(&networks);
     }
   }