Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/common/gcm_messages.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_GCM_DRIVER_COMMON_GCM_MESSAGES_H_
 #define COMPONENTS_GCM_DRIVER_COMMON_GCM_MESSAGES_H_
 
 #include <map>
 #include <string>
 
@@ skipping 20 matching lines @@
 
 // Message being received from the other party.
 struct GCM_DRIVER_EXPORT IncomingMessage {
   IncomingMessage();
   ~IncomingMessage();
 
   MessageData data;
   std::string collapse_key;
   std::string sender_id;
   std::string raw_data;
+
+  // Whether the contents of the message have been decrypted, and are
+  // available in |raw_data|.
+  bool decrypted;
 };
 
 }  // namespace gcm
 
 #endif  // COMPONENTS_GCM_DRIVER_COMMON_GCM_MESSAGES_H_