Use base namespace for string16 in chrome/renderer.

chrome/renderer/spellchecker/custom_dictionary_engine_unittest.cc

 // Copyright (c) 2013 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 "base/strings/utf_string_conversions.h"
 #include "chrome/renderer/spellchecker/custom_dictionary_engine.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(CustomDictionaryTest, HandlesEmptyWordWithInvalidSubstring) {
   CustomDictionaryEngine engine;
   std::set<std::string> custom_words;
   engine.Init(custom_words);
-  EXPECT_FALSE(engine.SpellCheckWord(string16().c_str(), 15, 23));
+  EXPECT_FALSE(engine.SpellCheckWord(base::string16().c_str(), 15, 23));
 }
 
 TEST(CustomDictionaryTest, Basic) {
   CustomDictionaryEngine engine;
   EXPECT_FALSE(engine.SpellCheckWord(ASCIIToUTF16("helllo").c_str(), 0, 6));
   std::set<std::string> custom_words;
   custom_words.insert("helllo");
   engine.Init(custom_words);
   EXPECT_TRUE(engine.SpellCheckWord(ASCIIToUTF16("helllo").c_str(), 0, 6));
 }
 
 TEST(CustomDictionaryTest, HandlesNullCharacters) {
   char16 data[4] = {'a', 0, 'b', 'c'};
   EXPECT_FALSE(CustomDictionaryEngine().SpellCheckWord(data, 1, 1));
 }