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

components/gcm_driver/gcm_client_impl.h

Index: components/gcm_driver/gcm_client_impl.h
diff --git a/components/gcm_driver/gcm_client_impl.h b/components/gcm_driver/gcm_client_impl.h
index 9e102154b86b20e1cbe8c7ac5d81432a36087b1f..21a464918b9cc3fdaf73aec8cd7dce36b979be81 100644
--- a/components/gcm_driver/gcm_client_impl.h
+++ b/components/gcm_driver/gcm_client_impl.h
@@ -51,6 +51,7 @@ namespace gcm {
 class CheckinRequest;
 class ConnectionFactory;
 class GCMClientImplTest;
+enum class GCMMessageStatus;
 
 // Helper class for building GCM internals. Allows tests to inject fake versions
 // as necessary.
@@ -152,6 +153,13 @@ class GCMClientImpl
   void OnDisconnected() override;
 
  private:
+  // Send a message to GCM with information about the final status of a
+  // previously received message. This can be run as a result of a callback
+  // being executed from an AppHandler.
+  virtual void SendMessageReceipt(const std::string& message_id,

[Peter Beverloo, 2017/02/08 17:09:09]

This shouldn't be declared as `virtual` - nothing overrides it.

[harkness, 2017/02/09 16:27:30]

Done.

+                                  const std::string& app_id,
+                                  GCMMessageStatus status);
+
   // The check-in info for the device.
   // TODO(fgorski): Convert to a class with explicit getters/setters.
   struct CheckinInfo {