Teach the GCM Driver how to decrypt incoming messages.

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 572c02d8b793d035901b76021e924d4dbd04f9de..169d751b2023bfdfa85db774477d896defb436ae 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -265,6 +265,12 @@ class GCMDriver {
 
   bool HasRegisterCallback(const std::string& app_id);
 
+  // Dispatches the OnMessage event to the app handler associated with |app_id|.
+  // If the |message| has been encrypted, it will be asynchronously decrypted
+  // before being dispatched to the handler associated with |app_id|.
+  void DispatchMessage(const std::string& app_id,
+                       const IncomingMessage& message);
+
   void ClearCallbacks();
 
  private:
@@ -281,6 +287,11 @@ class GCMDriver {
       const UnregisterCallback& unregister_callback,
       GCMClient::Result result);
 
+  // Dispatches |message| to |app_id| if the decryption was successful.
+  void DispatchDecryptedMessage(const std::string& app_id,

[jianli, 2015/08/04 00:49:30]

This method might also dispatch an error event in the future. So the name
DispatchDecryptedMessage does not reflect this potential new behavior. How about
DispatchMessageUponDecryption?

[Peter Beverloo, 2015/09/25 16:37:35]

This doesn't apply anymore due to re-using DispatchMessage().

+                                const IncomingMessage& message,
+                                bool decryption_successful);
+
   // Callback map (from app_id to callback) for Register.
   std::map<std::string, RegisterCallback> register_callbacks_;