Distinguish null IDBKey (no value) and invalid IDBKey (value is not valid key)

content/common/indexed_db/indexed_db_key.h

 // Copyright (c) 2011 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 CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_
 #define CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_
 #pragma once
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/string16.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebIDBKey.h"
 
 class CONTENT_EXPORT IndexedDBKey {
  public:
   IndexedDBKey(); // Defaults to WebKit::WebIDBKey::InvalidType.
   explicit IndexedDBKey(const WebKit::WebIDBKey& key);
   ~IndexedDBKey();
 
+  void SetNull();
   void SetInvalid();
   void SetArray(const std::vector<IndexedDBKey>& array);
   void SetString(const string16& string);
   void SetDate(double date);
   void SetNumber(double number);
   void Set(const WebKit::WebIDBKey& key);
 
   WebKit::WebIDBKey::Type type() const { return type_; }
   const std::vector<IndexedDBKey>& array() const { return array_; }
   const string16& string() const { return string_; }
   double date() const { return date_; }
   double number() const { return number_; }
 
   operator WebKit::WebIDBKey() const;
 
  private:
   WebKit::WebIDBKey::Type type_;
   std::vector<IndexedDBKey> array_;
   string16 string_;
   double date_;
   double number_;
 };
 
 #endif  // CONTENT_COMMON_INDEXED_DB_INDEXED_DB_KEY_H_