Provide a mechanism for the GCM driver to send message receipts to GCM.

components/gcm_driver/gcm_client_impl.cc

Index: components/gcm_driver/gcm_client_impl.cc
diff --git a/components/gcm_driver/gcm_client_impl.cc b/components/gcm_driver/gcm_client_impl.cc
index bd44af2c7a28b9843ef1b504b8618534dac6cb39..278ab15f77cb50c9be92dabf92a174176f614f23 100644
--- a/components/gcm_driver/gcm_client_impl.cc
+++ b/components/gcm_driver/gcm_client_impl.cc
@@ -1344,6 +1344,8 @@ void GCMClientImpl::HandleIncomingMessage(const gcm::MCSMessage& message) {
       HandleIncomingSendError(app_id, data_message_stanza, message_data);
       break;
     case UNKNOWN:
+      delegate_->OnMessageReceivedError(data_message_stanza.id(), app_id,
+                                        GCMClient::GCM_UNKNOWN_MESSAGE_TYPE);
       DVLOG(1) << "Unknown message_type received. Message ignored. "
                << "App ID: " << app_id << ".";
       break;
@@ -1404,10 +1406,14 @@ void GCMClientImpl::HandleIncomingDataMessage(
   recorder_.RecordDataMessageReceived(app_id, sender,
       data_message_stanza.ByteSize(), registered,
       GCMStatsRecorder::DATA_MESSAGE);
-  if (!registered)
+  if (!registered) {
+    delegate_->OnMessageReceivedError(app_id, data_message_stanza.id(),
+                                      GCMClient::GCM_INVALID_SUBTYPE);

[Peter Beverloo, 2016/12/15 19:24:24]

It's a bit unfortunate that we need to do the GCMClient -> GCMDriver ->
GCMClient hoop. Could we instead have SendMessageReceipt() live in the GCMClient
and propagate the callback to the GCMDriver? (I guess this means that the
callback has to be declared in the same file as the enumeration.)

An additional benefit here is that we can avoid constructing an OutgoingMessage
object for Android, and instead use more specialized handling.

(At least until we need _real_ support for outgoing messages, because now you're
signing yourself up to do that work.)

[harkness, 2016/12/21 17:23:37]

I've mostly moved things to the GCMClient now. It does simplify things to not
need to pass them through the Delegate.

     return;
+  }
 
   IncomingMessage incoming_message;
+  incoming_message.id = data_message_stanza.id();
   incoming_message.sender_id = data_message_stanza.from();
   if (data_message_stanza.has_token())
     incoming_message.collapse_key = data_message_stanza.token();