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

components/gcm_driver/gcm_client.h

Index: components/gcm_driver/gcm_client.h
diff --git a/components/gcm_driver/gcm_client.h b/components/gcm_driver/gcm_client.h
index c4dd12adc914375e3c8cf118e114589f292a7df5..5eb8938134c5c7555be88c94f68e1785d7f5c16f 100644
--- a/components/gcm_driver/gcm_client.h
+++ b/components/gcm_driver/gcm_client.h
@@ -71,6 +71,19 @@ class GCMClient {
     UNKNOWN_ERROR
   };
 
+  // Enumeration to be used for describing the final status of a GCM message.
+  enum GCMMessageStatus {

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

Let's move this to its own file. It's not clear to me what usage like the
following means ("for what"):

    GCMClient::GCM_SUCCESS

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

currently still in the GCMClient, but I'm planning to move it. Next upload.

+    // 0 reserved for success.
+    GCM_SUCCESS = 0,
+
+    // 1 - 99 reserved for GCMClient and GCMDriver error status.

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

nit: Let's make sure that we pull this separate from our class separation, and
have comments that can be reused elsewhere. ("The GCM Client"?)

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

Done.

+    GCM_INVALID_SUBTYPE = 1,
+    GCM_ENCRYPTION_FAILURE = 2,
+    GCM_UNKNOWN_MESSAGE_TYPE = 3,
+    GCM_NO_APP_HANDLER = 4,
+    GCM_INVALID_MESSAGE_TAG = 5,
+  };
+
   enum ChromePlatform {
     PLATFORM_WIN,
     PLATFORM_MAC,
@@ -176,6 +189,14 @@ class GCMClient {
     virtual void OnMessageReceived(const std::string& app_id,
                                    const IncomingMessage& message) = 0;
 
+    // Called when there is an error processing a received message.
+    // |app_id|: application ID.
+    // |message_id|: id of the message received.
+    // |status|: error type.
+    virtual void OnMessageReceivedError(const std::string& app_id,
+                                        const std::string& message_id,
+                                        int status) = 0;
+
     // Called when some messages have been deleted from the server.
     // |app_id|: application ID.
     virtual void OnMessagesDeleted(const std::string& app_id) = 0;