[remoting][FTL] Change message type to STATUS

The USER message class sends GCM tickle. We have never set up GCM
project nor do we rely on tickle, so this CL changes the message class
to STATUS, so that the FTL server doesn't send a tickle to the receiver
for signaling messages.

Bug: 992563
Change-Id: Ie3528b9586ef67115a7ccfa5782461aad9167dc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1757068
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691433}

remoting/proto/ftl/v1/ftl_messages.proto

@@ -143,7 +143,10 @@ message InboxMessage {
     CHROMOTING_MESSAGE = 29;
   }
 
-  enum MessageClass { USER = 0; }
+  enum MessageClass {
+    USER = 0;    // USER both persists the message and sends a GCM tickle
+    STATUS = 3;  // STATUS persists the message and doesn't send GCM tickle
+  }
 
   string message_id = 1;
   MessageType message_type = 2;

remoting/signaling/ftl_messaging_client.cc

@@ -103,7 +103,7 @@ void FtlMessagingClient::SendMessage(
   request.mutable_message()->set_message_type(
       ftl::InboxMessage_MessageType_CHROMOTING_MESSAGE);
   request.mutable_message()->set_message_class(
-      ftl::InboxMessage_MessageClass_USER);
+      ftl::InboxMessage_MessageClass_STATUS);
   if (!destination_registration_id.empty()) {
     request.add_dest_registration_ids(destination_registration_id);
   }