extensions: Cleanup class/struct fwd declarations

extensions/common/permissions/api_permission_set.h

 // Copyright 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 EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_SET_H_
 #define EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_SET_H_
 
 #include <stddef.h>
 
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/strings/string16.h"
 #include "extensions/common/permissions/api_permission.h"
 #include "extensions/common/permissions/base_set_operators.h"
 
 namespace base {
 class ListValue;
 }  // namespace base
 
 namespace extensions {
 
 class APIPermissionSet;
-class Extension;
 
 template<>
 struct BaseSetOperatorsTraits<APIPermissionSet> {
   typedef APIPermission ElementType;
   typedef APIPermission::ID ElementIDType;
 };
 
 class APIPermissionSet : public BaseSetOperators<APIPermissionSet> {
  public:
   enum ParseSource {
@@ skipping 127 matching lines @@
 
  private:
   explicit PermissionIDSet(const std::set<PermissionID>& permissions);
 
   std::set<PermissionID> permissions_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_SET_H_