[GCM] Incoming GCM message without type should be treated as data mes…

…sage

BUG=353363
TEST=Manual test by following repro steps
R=zea@chromium.org

Review URL: https://codereview.chromium.org/200763009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257546 0039d316-1c4b-4281-b951-d872f2087c98

google_apis/gcm/gcm_client_impl.cc

@@ -510,7 +510,7 @@ void GCMClientImpl::HandleIncomingMessage(const gcm::MCSMessage& message) {
     message_data[key] = data_message_stanza.app_data(i).value();
   }
 
-  MessageType message_type = UNKNOWN;
+  MessageType message_type = DATA_MESSAGE;
   MessageData::iterator iter = message_data.find(kMessageTypeKey);
   if (iter != message_data.end()) {
     message_type = DecodeMessageType(iter->second);