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

net/http/http_server_properties_impl.cc

Index: net/http/http_server_properties_impl.cc
diff --git a/net/http/http_server_properties_impl.cc b/net/http/http_server_properties_impl.cc
index a0a6bfe644f35fbde0ac8fb00d0c1a98d830f307..ab2088f0f65d6d321dfeaa812444260031c70444 100644
--- a/net/http/http_server_properties_impl.cc
+++ b/net/http/http_server_properties_impl.cc
@@ -32,6 +32,7 @@
       alternative_service_map_(AlternativeServiceMap::NO_AUTO_EVICT),
       spdy_settings_map_(SpdySettingsMap::NO_AUTO_EVICT),
       server_network_stats_map_(ServerNetworkStatsMap::NO_AUTO_EVICT),
+      alternative_service_probability_threshold_(1.0),
       quic_server_info_map_(QuicServerInfoMap::NO_AUTO_EVICT),
       max_server_configs_stored_in_properties_(kMaxQuicServersToPersist),
       weak_ptr_factory_(this) {
@@ -322,8 +323,9 @@
 
 AlternativeServiceVector HttpServerPropertiesImpl::GetAlternativeServices(
     const HostPortPair& origin) {
-  // Copy valid alternative services into |valid_alternative_services|.
-  AlternativeServiceVector valid_alternative_services;
+  // Copy alternative services with probability greater than or equal to the
+  // threshold into |alternative_services_above_threshold|.
+  AlternativeServiceVector alternative_services_above_threshold;
   const base::Time now = base::Time::Now();
   AlternativeServiceMap::iterator map_it = alternative_service_map_.Get(origin);
   if (map_it != alternative_service_map_.end()) {
@@ -333,6 +335,11 @@
         it = map_it->second.erase(it);
         continue;
       }
+      if (it->probability == 0 ||
+          it->probability < alternative_service_probability_threshold_) {
+        ++it;
+        continue;
+      }
       AlternativeService alternative_service(it->alternative_service);
       if (alternative_service.host.empty()) {
         alternative_service.host = origin.host();
@@ -346,13 +353,13 @@
         ++it;
         continue;
       }
-      valid_alternative_services.push_back(alternative_service);
+      alternative_services_above_threshold.push_back(alternative_service);
       ++it;
     }
     if (map_it->second.empty()) {
       alternative_service_map_.Erase(map_it);
     }
-    return valid_alternative_services;
+    return alternative_services_above_threshold;
   }
 
   CanonicalHostMap::const_iterator canonical = GetCanonicalHost(origin);
@@ -367,6 +374,10 @@
        it != map_it->second.end();) {
     if (it->expiration < now) {
       it = map_it->second.erase(it);
+      continue;
+    }
+    if (it->probability < alternative_service_probability_threshold_) {
+      ++it;
       continue;
     }
     AlternativeService alternative_service(it->alternative_service);
@@ -381,23 +392,25 @@
       ++it;
       continue;
     }
-    valid_alternative_services.push_back(alternative_service);
+    alternative_services_above_threshold.push_back(alternative_service);
     ++it;
   }
   if (map_it->second.empty()) {
     alternative_service_map_.Erase(map_it);
   }
-  return valid_alternative_services;
+  return alternative_services_above_threshold;
 }
 
 bool HttpServerPropertiesImpl::SetAlternativeService(
     const HostPortPair& origin,
     const AlternativeService& alternative_service,
+    double alternative_probability,
     base::Time expiration) {
   return SetAlternativeServices(
-      origin,
-      AlternativeServiceInfoVector(
-          /*size=*/1, AlternativeServiceInfo(alternative_service, expiration)));
+      origin, AlternativeServiceInfoVector(
+                  /*size=*/1,
+                  AlternativeServiceInfo(alternative_service,
+                                         alternative_probability, expiration)));
 }
 
 bool HttpServerPropertiesImpl::SetAlternativeServices(
@@ -682,6 +695,11 @@
   }
 
   quic_server_info_map_.Swap(temp_map);
+}
+
+void HttpServerPropertiesImpl::SetAlternativeServiceProbabilityThreshold(
+    double threshold) {
+  alternative_service_probability_threshold_ = threshold;
 }
 
 AlternativeServiceMap::const_iterator