[GCM] API update to allow only a single sender in registration

google_apis/gcm/gcm_client.h

Index: google_apis/gcm/gcm_client.h
diff --git a/google_apis/gcm/gcm_client.h b/google_apis/gcm/gcm_client.h
index 15f67cf21665f061bc03a903440ae68ac5666c12..eee1dd557ea884e7819e7b1df102b68db3951892 100644
--- a/google_apis/gcm/gcm_client.h
+++ b/google_apis/gcm/gcm_client.h
@@ -163,12 +163,12 @@ class GCM_EXPORT GCMClient {
   // called asynchronously upon completion.
   // |app_id|: application ID.
   // |cert|: SHA-1 of public key of the application, in base16 format.
-  // |sender_ids|: list of IDs of the servers that are allowed to send the
-  //               messages to the application. These IDs are assigned by the
-  //               Google API Console.
+  // |sender_id|: project ID of a server that is allowed to send messages to the
+  //              application. Project IDs are assigned by the Google API
+  //              Console.
   virtual void Register(const std::string& app_id,
                         const std::string& cert,
-                        const std::vector<std::string>& sender_ids) = 0;
+                        const std::string& sender_id) = 0;
 
   // Unregisters the application from GCM when it is uninstalled.
   // Delegate::OnUnregisterFinished will be called asynchronously upon