Minor C++ fixes found by Clang.

printing/pdf_ps_metafile_cairo.h

 // Copyright (c) 2009 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_PDF_PS_METAFILE_CAIRO_H_
 #define PRINTING_PDF_PS_METAFILE_CAIRO_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 
 typedef struct _cairo_surface cairo_surface_t;
 typedef struct _cairo cairo_t;
 
 namespace base {
-class FileDescriptor;
+struct FileDescriptor;
 }
 
 class FilePath;
 
 namespace printing {
 
 // This class uses Cairo graphics library to generate PostScript/PDF stream
 // and stores rendering results in a string buffer.
 class PdfPsMetafile {
  public:
@@ skipping 74 matching lines @@
 
   // Buffer stores PDF/PS contents for current page only.
   std::string current_page_;
 
   DISALLOW_COPY_AND_ASSIGN(PdfPsMetafile);
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_PDF_PS_METAFILE_CAIRO_H_