Use a direct include of strings headers in content/p*/.

content/plugin/plugin_main_mac.mm

 // 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.
 
 #import <AppKit/AppKit.h>
 
 #include "base/environment.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "content/common/plugin_carbon_interpose_constants_mac.h"
 #include "content/plugin/plugin_interpose_util_mac.h"
 #include "content/public/common/content_client.h"
 
 namespace content {
 
 #if !defined(__LP64__)
 void TrimInterposeEnvironment() {
   scoped_ptr<base::Environment> env(base::Environment::Create());
 
@@ skipping 24 matching lines @@
   }
 }
 #endif
 
 void InitializeChromeApplication() {
   [NSApplication sharedApplication];
   mac_plugin_interposing::SetUpCocoaInterposing();
 }
 
 }  // namespace content