Introduce State to DriveIntegrationService.

chrome/browser/chromeos/drive/file_system.cc

 // Copyright (c) 2012 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 "chrome/browser/chromeos/drive/file_system.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/platform_file.h"
@@ skipping 383 matching lines @@
   DVLOG(1) << "CheckForUpdates finished: " << FileErrorToString(error);
   last_update_check_time_ = base::Time::Now();
   last_update_check_error_ = error;
 }
 
 FileSystem::~FileSystem() {
   // This should be called from UI thread, from DriveIntegrationService
   // shutdown.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  change_list_loader_->RemoveObserver(this);
+  if (change_list_loader_)
+    change_list_loader_->RemoveObserver(this);
 }
 
 void FileSystem::AddObserver(FileSystemObserver* observer) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   observers_.AddObserver(observer);
 }
 
 void FileSystem::RemoveObserver(FileSystemObserver* observer) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   observers_.RemoveObserver(observer);
@@ skipping 674 matching lines @@
   if (util::IsSpecialResourceId(id))
     return;
 
   util::Log(logging::LOG_INFO,
             "Thumbnail refresh for %s", directory_path.AsUTF8Unsafe().c_str());
   change_list_loader_->LoadDirectoryFromServer(
       id, base::Bind(&util::EmptyFileOperationCallback));
 }
 
 }  // namespace drive