Use a direct include of strings headers, delete some strings forwarding headers.

content/test/accessibility_browser_test_utils.cc

 // Copyright 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 "content/test/accessibility_browser_test_utils.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/port/browser/render_widget_host_view_port.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/test/test_utils.h"
 #include "content/shell/shell.h"
 
 namespace content {
 
@@ skipping 42 matching lines @@
   iter = root.string_attributes.find(AccessibilityNodeData::ATTR_DOC_URL);
   if (iter != root.string_attributes.end()) {
     string16 doc_url = iter->second;
     if (doc_url == ASCIIToUTF16(kAboutBlankURL))
       return true;
   }
   return false;
 }
 
 }  // namespace content