Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/common/gcm_messages.cc

 // 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.
 
 #include "components/gcm_driver/common/gcm_messages.h"
 
 namespace gcm {
 
 // static
 const int OutgoingMessage::kMaximumTTL = 24 * 60 * 60;  // 1 day.
 
 OutgoingMessage::OutgoingMessage() : time_to_live(kMaximumTTL) {
 }
 
 OutgoingMessage::~OutgoingMessage() {
 }
 
-IncomingMessage::IncomingMessage() {
+IncomingMessage::IncomingMessage() : decrypted(false) {
 }
 
 IncomingMessage::~IncomingMessage() {
 }
 
 }  // namespace gcm