Add a nullable string16 class to base. It combines a string16 + a null param...

base/nullable_string16.h

+// Copyright (c) 2009 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 BASE_NULLABLE_STRING16_H_
+#define BASE_NULLABLE_STRING16_H_
+
+#include "base/string16.h"
+
+// This class is a simple wrapper for string16 which also contains a null
+// state.  This should be used only where the difference between null and
+// empty is meaningful.
+class NullableString16 {
+ public:
+  NullableString16() : is_null_(false) { }
+  NullableString16(const string16& string, bool is_null)
+      : string_(string), is_null_(is_null) {
+  }
+
+  const string16& string() const { return string_; }
+  bool is_null() const { return is_null_; }
+
+ private:
+  string16 string_;
+  bool is_null_;
+};
+
+#endif  // BASE_NULLABLE_STRING16_H_