Use a direct include of strings headers in testing/, third_party/, tools/.

tools/imagediff/image_diff.cc

 // 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.
 
 // This file input format is based loosely on
 // Tools/DumpRenderTree/ImageDiff.m
 
 // The exact format of this tool's output to stdout is important, to match
 // what the run-webkit-tests script expects.
 
 #include <algorithm>
 #include <iostream>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/process_util.h"
 #include "base/safe_numerics.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/size.h"
 
 #if defined(OS_WIN)
 #include "windows.h"
 #endif
 
 // Causes the app to remain open, waiting for pairs of filenames on stdin.
 // The caller is then responsible for terminating this app.
@@ skipping 340 matching lines @@
                         base::FilePath(args[1]),
                         base::FilePath(args[2]));
     }
   } else if (args.size() == 2) {
     return CompareImages(base::FilePath(args[0]), base::FilePath(args[1]));
   }
 
   PrintHelp();
   return kStatusError;
 }