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

chrome/renderer/plugins/plugin_placeholder.cc

 // 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.
 
 #include "chrome/renderer/plugins/plugin_placeholder.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/json/string_escape.h"
-#include "base/string_util.h"
 #include "base/strings/string_piece.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/common/prerender_messages.h"
 #include "chrome/common/render_messages.h"
 #include "chrome/renderer/chrome_content_renderer_client.h"
 #include "chrome/renderer/custom_menu_commands.h"
 #include "chrome/renderer/plugins/plugin_uma.h"
 #include "content/public/common/context_menu_params.h"
 #include "content/public/renderer/render_thread.h"
 #include "content/public/renderer/render_view.h"
@@ skipping 610 matching lines @@
 bool PluginPlaceholder::IsYouTubeURL(const GURL& url,
                                        const std::string& mime_type) {
   std::string host = url.host();
   bool is_youtube = EndsWith(host, "youtube.com", true) ||
       EndsWith(host, "youtube-nocookie.com", true);
 
   return is_youtube && IsValidYouTubeVideo(url.path()) &&
       LowerCaseEqualsASCII(mime_type, kFlashPluginSwfMimeType);
 }
 #endif