Create a new preference which disables UDP protocol for WebRTC

content/renderer/p2p/port_allocator.h

Index: content/renderer/p2p/port_allocator.h
diff --git a/content/renderer/p2p/port_allocator.h b/content/renderer/p2p/port_allocator.h
index 3d1ae5fa161a85cc81d6ea66a3e2f8ea9b1631f2..84f65b9c2f40b1f805a7f1c09b20961ce3864b1e 100644
--- a/content/renderer/p2p/port_allocator.h
+++ b/content/renderer/p2p/port_allocator.h
@@ -35,11 +35,14 @@ class P2PPortAllocator : public cricket::BasicPortAllocator {
 
     std::vector<RelayServerConfig> relays;
 
-    // Disable TCP-based transport when set to true.
-    bool disable_tcp_transport;
+    // Disable TCP-based transport when set to false.

[juberti1, 2015/08/27 00:21:20]

This is somewhat confusing because enable_tcp_transport is subtly different than
enable_nonproxied_udp_transport. i.e., TCP transport set to false allows TCP
transport to relay, but UDP transport set to false doesn't allow UDP transport
to relay.

I think the key issue is the use of the word |transport|, since disabling
TcpPort is different than disabling *all UDP traffic*.

[pthatcher2, 2015/08/27 16:59:09]

That's a good point.  But since TCP to the relay would go through a proxy, we
could name it "enable_nonproxied_tcp" to match "enable_unproxied_udp", couldn't
we?  Then they would be consistent.

I agree with dropping the word "transport".  I don't like it.

+    bool enable_tcp_transport = true;
+
+    // Disable non-proxied UPD-based transport when set to false.

[juberti1, 2015/08/27 00:21:20]

UDP

+    bool enable_nonproxied_udp_transport = true;
 
     // Disable binding to individual NICs when set to false.
-    bool enable_multiple_routes;
+    bool enable_multiple_routes = true;
   };
 
   P2PPortAllocator(P2PSocketDispatcher* socket_dispatcher,