Use a direct include of strings headers in chrome/renderer/.

chrome/renderer/spellchecker/custom_dictionary_engine.h

 // 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.
 
 #ifndef CHROME_RENDERER_SPELLCHECKER_CUSTOM_DICTIONARY_ENGINE_H_
 #define CHROME_RENDERER_SPELLCHECKER_CUSTOM_DICTIONARY_ENGINE_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 // Custom spellcheck dictionary. Words in this dictionary are always correctly
 // spelled. Words that are not in this dictionary may or may not be correctly
 // spelled.
 class CustomDictionaryEngine {
  public:
   CustomDictionaryEngine();
   ~CustomDictionaryEngine();
 
   // Initialize the custom dictionary engine.
@@ skipping 12 matching lines @@
       const std::vector<std::string>& words_removed);
 
  private:
   // Correctly spelled words.
   std::set<string16> dictionary_;
 
   DISALLOW_COPY_AND_ASSIGN(CustomDictionaryEngine);
 };
 
 #endif  // CHROME_RENDERER_SPELLCHECKER_CUSTOM_DICTIONARY_ENGINE_H_