Generate Instance ID locally.

components/gcm_driver/instance_id/instance_id_impl.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_INSTANCE_ID_INSTANCE_ID_IMPL_H_
 #define COMPONENTS_GCM_DRIVER_INSTANCE_ID_INSTANCE_ID_IMPL_H_
 
 #include <map>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "components/gcm_driver/instance_id/instance_id.h"
 
 namespace instance_id {
 
 // InstanceID implementation for desktop and iOS.
 class InstanceIDImpl : public InstanceID {
  public:
   explicit InstanceIDImpl(const std::string& app_id);
   ~InstanceIDImpl() override;
 
   // InstanceID:
   std::string GetID() override;
   base::Time GetCreationTime() override;
   void GetToken(const std::string& audience,
                 const std::string& scope,
                 const std::map<std::string, std::string>& options,
                 const GetTokenCallback& callback) override;
   void DeleteToken(const std::string& audience,
                    const std::string& scope,
                    const DeleteTokenCallback& callback) override;
   void DeleteID(const DeleteIDCallback& callback) override;
 
  private:
+  void EnsureIDGenerated();
+
+  // The generated Instance ID.
+  std::string id_;
+
+  // The time when the Instance ID has been generated.
+  base::Time creation_time_;
+
   DISALLOW_COPY_AND_ASSIGN(InstanceIDImpl);
 };
 
 }  // namespace instance_id
 
 #endif  // COMPONENTS_GCM_DRIVER_INSTANCE_ID_INSTANCE_ID_IMPL_H_