ppapi: Cleanup class/struct forward declarations

ppapi/cpp/private/pdf.h

 // Copyright (c) 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.
 
 #ifndef PPAPI_CPP_PRIVATE_PDF_H_
 #define PPAPI_CPP_PRIVATE_PDF_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "ppapi/c/private/ppb_pdf.h"
 
 struct PP_BrowserFont_Trusted_Description;
 
 namespace pp {
 
-class ImageData;
 class InstanceHandle;
 class Var;
 
 class PDF {
  public:
   // Returns true if the required interface is available.
   static bool IsAvailable();
 
   static PP_Resource GetFontFileWithFallback(
       const InstanceHandle& instance,
@@ skipping 41 matching lines @@
       PP_PrivateAccessibilityTextRunInfo text_runs[],
       PP_PrivateAccessibilityCharInfo chars[]);
   static void SetCrashData(const InstanceHandle& instance,
                            const char* pdf_url,
                            const char* top_level_url);
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_PRIVATE_PDF_H_