Revert of Remove support for Alt-Svc/Alternate Protocol Probability

net/http/http_stream_factory.cc

Index: net/http/http_stream_factory.cc
diff --git a/net/http/http_stream_factory.cc b/net/http/http_stream_factory.cc
index bc0212b381e8ae295bc2366d8c5cf43ae36ce475..d6d76b453c8e82d124d474ad7c844d3f5a1f5ade 100644
--- a/net/http/http_stream_factory.cc
+++ b/net/http/http_stream_factory.cc
@@ -79,8 +79,8 @@
     base::Time expiration =
         base::Time::Now() +
         base::TimeDelta::FromSeconds(alternative_service_entry.max_age);
-    AlternativeServiceInfo alternative_service_info(alternative_service,
-                                                    expiration);
+    AlternativeServiceInfo alternative_service_info(
+        alternative_service, alternative_service_entry.probability, expiration);
     alternative_service_info_vector.push_back(alternative_service_info);
   }
 
@@ -95,9 +95,24 @@
     const HttpNetworkSession& session) {
   AlternateProtocol protocol = UNINITIALIZED_ALTERNATE_PROTOCOL;
   int port = 0;
+  double probability = 1;
   bool is_valid = true;
   for (size_t i = 0; i < alternate_protocol_values.size(); ++i) {
     base::StringPiece alternate_protocol_str = alternate_protocol_values[i];
+    if (base::StartsWith(alternate_protocol_str, "p=",
+                         base::CompareCase::SENSITIVE)) {
+      if (!base::StringToDouble(alternate_protocol_str.substr(2).as_string(),
+                                &probability) ||
+          probability < 0 || probability > 1) {
+        DVLOG(1) << kAlternateProtocolHeader
+                 << " header has unrecognizable probability: "
+                 << alternate_protocol_values[i];
+        is_valid = false;
+        break;
+      }
+      continue;
+    }
+
     std::vector<base::StringPiece> port_protocol_vector =
         base::SplitStringPiece(alternate_protocol_str, ":",
                                base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
@@ -138,7 +153,7 @@
   http_server_properties->SetAlternativeService(
       RewriteHost(http_host_port_pair),
       AlternativeService(protocol, "", static_cast<uint16_t>(port)),
-      base::Time::Now() + base::TimeDelta::FromDays(30));
+      probability, base::Time::Now() + base::TimeDelta::FromDays(30));
 }
 
 GURL HttpStreamFactory::ApplyHostMappingRules(const GURL& url,