[GCM] Add port 443 fallback logic and histograms

google_apis/gcm/gcm_client_impl.cc

Index: google_apis/gcm/gcm_client_impl.cc
diff --git a/google_apis/gcm/gcm_client_impl.cc b/google_apis/gcm/gcm_client_impl.cc
index ad02a4d80d36cc04ba0624dfb2a59f3239980447..325226fc1602989e1a3876192df7495fdf971908 100644
--- a/google_apis/gcm/gcm_client_impl.cc
+++ b/google_apis/gcm/gcm_client_impl.cc
@@ -67,7 +67,13 @@ enum MessageType {
   SEND_ERROR,        // Error sending a message.
 };
 
-const char kMCSEndpoint[] = "https://mtalk.google.com:5228";
+// MCS endpoints. SSL Key pinning is done automatically due to the *.google.com
+// pinning rule.
+// Note: modifying the endpoints will affect the ability to compare the
+// GCM.CurrentEnpoint histogram across versions.
+const char kMCSEndpointMain[] = "https://mtalk.google.com:5228";
+const char kMCSEndpointFallback[] = "https://mtalk.google.com:443";
+
 const int kMaxRegistrationRetries = 5;
 const char kMessageTypeDataMessage[] = "gcm";
 const char kMessageTypeDeletedMessagesKey[] = "deleted_messages";
@@ -189,8 +195,11 @@ void GCMClientImpl::InitializeMCSClient(
             GetNetworkSessionParams();
     DCHECK(network_session_params);
     network_session_ = new net::HttpNetworkSession(*network_session_params);
+    std::vector<GURL> endpoints;
+    endpoints.push_back(GURL(kMCSEndpointMain));
+    endpoints.push_back(GURL(kMCSEndpointFallback));
     connection_factory_.reset(new ConnectionFactoryImpl(
-        GURL(kMCSEndpoint),
+        endpoints,
         kDefaultBackoffPolicy,
         network_session_,
         net_log_.net_log()));