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..a86af93343072ba242f6a917a2b4811690779205 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -18,6 +18,7 @@
 #include "components/gcm_driver/crypto/gcm_encryption_provider.h"
 #include "components/gcm_driver/default_gcm_app_handler.h"
 #include "components/gcm_driver/gcm_client.h"
+#include "components/gcm_driver/gcm_message_status.h"
 
 namespace base {
 class FilePath;
@@ -199,7 +200,7 @@ 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 +293,8 @@ 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 MessageReceiptCallback& receipt_callback);
 
  private:
   // Common code shared by Unregister and UnregisterWithSenderId.
@@ -304,6 +306,7 @@ class GCMDriver {
   // 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,
+                               const MessageReceiptCallback& receipt_callback,
                                GCMEncryptionProvider::DecryptionResult result,
                                const IncomingMessage& message);