Add a probability to Alternate-Protocol support.

net/http/http_server_properties.cc

Index: net/http/http_server_properties.cc
diff --git a/net/http/http_server_properties.cc b/net/http/http_server_properties.cc
index 1a9bfb6180e3c7d1285d7411cd998f38a987a4d9..abc5cb1843659d5bcc33d232508f2f7cdbc8978b 100644
--- a/net/http/http_server_properties.cc
+++ b/net/http/http_server_properties.cc
@@ -111,9 +111,10 @@ AlternateProtocol AlternateProtocolFromNextProto(NextProto next_proto) {
   return UNINITIALIZED_ALTERNATE_PROTOCOL;
 }
 
-std::string PortAlternateProtocolPair::ToString() const {
-  return base::StringPrintf("%d:%s", port,
-                            AlternateProtocolToString(protocol));
+std::string AlternateProtocolInfo::ToString() const {
+  return base::StringPrintf("%d:%s p=%f", port,
+                            AlternateProtocolToString(protocol),
+                            probability);
 }
 
 }  // namespace net