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

components/gcm_driver/gcm_driver.h

Index: components/gcm_driver/gcm_driver.h
diff --git a/components/gcm_driver/gcm_driver.h b/components/gcm_driver/gcm_driver.h
index f115d16562a00f5259063fee96ca738bf8819c74..4ca788e6317e28b6591a68b2c3cf40d0aa47e001 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -199,7 +199,7 @@ class GCMDriver {
   // Updates the |account_mapping| information in persistent store.
   virtual void UpdateAccountMapping(const AccountMapping& account_mapping) = 0;
 
-  // Removes the account mapping information reated to |account_id| from
+  // Removes the account mapping information related to |account_id| from
   // persistent store.
   virtual void RemoveAccountMapping(const std::string& account_id) = 0;
 
@@ -292,7 +292,8 @@ class GCMDriver {
   // dispatched when the decryption operation was successful. Otherwise, the
   // |message| will be dispatched immediately to the handler for |app_id|.
   void DispatchMessage(const std::string& app_id,
-                       const IncomingMessage& message);
+                       const IncomingMessage& message,
+                       const GCMClient::MessageReceiptCallback& callback);
 
  private:
   // Common code shared by Unregister and UnregisterWithSenderId.
@@ -303,9 +304,11 @@ class GCMDriver {
   // Dispatches the OnMessage event to the app handler associated with |app_id|
   // if |result| indicates that it is safe to do so, or will report a decryption
   // failure for the |app_id| otherwise.
-  void DispatchMessageInternal(const std::string& app_id,
-                               GCMEncryptionProvider::DecryptionResult result,
-                               const IncomingMessage& message);
+  void DispatchMessageInternal(
+      const std::string& app_id,
+      const GCMClient::MessageReceiptCallback& callback,
+      GCMEncryptionProvider::DecryptionResult result,
+      const IncomingMessage& message);
 
   // Called after unregistration completes in order to trigger the pending
   // registration.