Use a direct include of strings headers in base/.

base/strings/string_split.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 BASE_STRINGS_STRING_SPLIT_H_
 #define BASE_STRINGS_STRING_SPLIT_H_
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/base_export.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace base {
 
 // Splits |str| into a vector of strings delimited by |s|, placing the results
 // in |r|. If several instances of |s| are contiguous, or if |str| begins with
 // or ends with |s|, then an empty string is inserted.
 //
 // Every substring is trimmed of any leading or trailing white space.
 // NOTE: |c| must be in BMP (Basic Multilingual Plane)
 BASE_EXPORT void SplitString(const string16& str,
@@ skipping 48 matching lines @@
 // characters defined by HTML 5). Each contiguous block of non-whitespace
 // characters is added to result.
 BASE_EXPORT void SplitStringAlongWhitespace(const string16& str,
                                             std::vector<string16>* result);
 BASE_EXPORT void SplitStringAlongWhitespace(const std::string& str,
                                             std::vector<std::string>* result);
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_STRING_SPLIT_H_