Changing SessionService to have a BaseSessionService, not being one.

chrome/browser/sessions/base_session_service_delegate_impl.h

 // Copyright 2014 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 CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_DELEGATE_IMPL_H_
 #define CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_DELEGATE_IMPL_H_
 
 #include "chrome/browser/sessions/base_session_service_delegate.h"
 
 class BaseSessionServiceDelegateImpl : public BaseSessionServiceDelegate {
  public:
   // If |use_delayed_save| is true, save operations can be performed as a
   // delayed task. Generally |used_delayed_save| should be true, testing may
   // supply false.
   explicit BaseSessionServiceDelegateImpl(bool should_use_delayed_save);
   ~BaseSessionServiceDelegateImpl() override {}
 
   // BaseSessionServiceDelegate:
   base::SequencedWorkerPool* GetBlockingPool() override;
   bool ShouldTrackEntry(const GURL& url) override;
   bool ShouldUseDelayedSave() override;
+  void OnWillSaveCommands() override {}
+  void OnSavedCommands() override {}
 
  private:
   // True if save operations can be performed as a delayed task. This can be
   // disabled for unit tests.
   const bool should_use_delayed_save_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseSessionServiceDelegateImpl);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_DELEGATE_IMPL_H_