Use a direct include of strings headers in ppapi/, printing/.

printing/printed_document.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 PRINTING_PRINTED_DOCUMENT_H_
 #define PRINTING_PRINTED_DOCUMENT_H_
 
 #include <map>
 
 #include "base/memory/ref_counted.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/synchronization/lock.h"
 #include "printing/print_settings.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace base {
 class FilePath;
 class MessageLoop;
 }
 
 namespace printing {
@@ skipping 149 matching lines @@
 
   // All the immutable members.
   const Immutable immutable_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintedDocument);
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_PRINTED_DOCUMENT_H_