Cleanup remaining class/struct fwd declarations

gin/function_template.h

 // Copyright 2014 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 GIN_FUNCTION_TEMPLATE_H_
 #define GIN_FUNCTION_TEMPLATE_H_
 
 #include <stddef.h>
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "gin/arguments.h"
 #include "gin/converter.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
-class PerIsolateData;
-
 enum CreateFunctionTemplateFlags {
   HolderIsFirstArgument = 1 << 0,
 };
 
 namespace internal {
 
 template<typename T>
 struct CallbackParamTraits {
   typedef T LocalType;
 };
@@ skipping 223 matching lines @@
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);
   tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
                                  ConvertToV8<v8::Local<v8::External> >(
                                      isolate, holder->GetHandle(isolate)));
 }
 
 }  // namespace gin
 
 #endif  // GIN_FUNCTION_TEMPLATE_H_