ppapi: Cleanup class/struct forward declarations

ppapi/cpp/dev/file_chooser_dev.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 PPAPI_CPP_DEV_FILE_CHOOSER_DEV_H_
 #define PPAPI_CPP_DEV_FILE_CHOOSER_DEV_H_
 
 #include <stdint.h>
 
 #include <vector>
 
 #include "ppapi/c/dev/ppb_file_chooser_dev.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/file_ref.h"
 #include "ppapi/cpp/resource.h"
 
 namespace pp {
 
-class CompletionCallback;
 class FileRef;
 class InstanceHandle;
 class Var;
 
 class FileChooser_Dev : public Resource {
  public:
   /// Creates an is_null() FileChooser object.
   FileChooser_Dev() {}
 
   /// This function creates a file chooser dialog resource.  The chooser is
@@ skipping 63 matching lines @@
   // the caller is expecting.
   //
   // This takes a heap-allocated ChooseCallbackData0_5 struct passed as the
   // user data and deletes it when the call completes.
   static void CallbackConverter(void* user_data, int32_t result);
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_FILE_CHOOSER_DEV_H_