Move nullable_string16.h to the string subdirectory.

webkit/browser/dom_storage/dom_storage_context.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 "webkit/browser/dom_storage/dom_storage_context.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/file_util.h"
 #include "base/files/file_enumerator.h"
@@ skipping 192 matching lines @@
 }
 
 void DomStorageContext::RemoveEventObserver(EventObserver* observer) {
   event_observers_.RemoveObserver(observer);
 }
 
 void DomStorageContext::NotifyItemSet(
     const DomStorageArea* area,
     const base::string16& key,
     const base::string16& new_value,
-    const NullableString16& old_value,
+    const base::NullableString16& old_value,
     const GURL& page_url) {
   FOR_EACH_OBSERVER(
       EventObserver, event_observers_,
       OnDomStorageItemSet(area, key, new_value, old_value, page_url));
 }
 
 void DomStorageContext::NotifyItemRemoved(
     const DomStorageArea* area,
     const base::string16& key,
     const base::string16& old_value,
@@ skipping 189 matching lines @@
   if (!deletable_persistent_namespace_ids_.empty()) {
     task_runner_->PostDelayedTask(
         FROM_HERE, base::Bind(
             &DomStorageContext::DeleteNextUnusedNamespace,
             this),
         base::TimeDelta::FromSeconds(kSessionStoraceScavengingSeconds));
   }
 }
 
 }  // namespace dom_storage