[GCM] Only allow the senders that the application is currently registered for

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 640977afb806f28efd0624d4a181f0d7495b2a5c..8bfa624fb7cdd838fe18f2b3e99d94e3681c24dc 100644
--- a/google_apis/gcm/gcm_client_impl.cc
+++ b/google_apis/gcm/gcm_client_impl.cc
@@ -456,9 +456,13 @@ void GCMClientImpl::OnMCSError() {
 }
 
 void GCMClientImpl::HandleIncomingMessage(const gcm::MCSMessage& message) {
+  DCHECK(delegate_);
+
   const mcs_proto::DataMessageStanza& data_message_stanza =
       reinterpret_cast<const mcs_proto::DataMessageStanza&>(
           message.GetProtobuf());
+  DCHECK_EQ(data_message_stanza.device_user_id(), kDefaultUserSerialNumber);
+
   IncomingMessage incoming_message;
   MessageType message_type = DATA_MESSAGE;
   for (int i = 0; i < data_message_stanza.app_data_size(); ++i) {
@@ -469,14 +473,12 @@ void GCMClientImpl::HandleIncomingMessage(const gcm::MCSMessage& message) {
       incoming_message.data[key] = data_message_stanza.app_data(i).value();
   }
 
-  if (data_message_stanza.has_token())
-    incoming_message.collapse_key = data_message_stanza.token();
-
-  DCHECK_EQ(data_message_stanza.device_user_id(), kDefaultUserSerialNumber);
-  DCHECK(delegate_);
 
   switch (message_type) {
     case DATA_MESSAGE:
+      incoming_message.sender_id = data_message_stanza.from();
+      if (data_message_stanza.has_token())
+        incoming_message.collapse_key = data_message_stanza.token();
       delegate_->OnMessageReceived(data_message_stanza.category(),
                                    incoming_message);
       break;