extensions: Cleanup class/struct fwd declarations

extensions/common/api/declarative/declarative_manifest_handler.h

 // Copyright 2015 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_API_DECLARATIVE_DECLARATIVE_MANIFEST_HANDLER_H_
 #define EXTENSIONS_COMMON_API_DECLARATIVE_DECLARATIVE_MANIFEST_HANDLER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "extensions/common/manifest_handler.h"
 
 namespace extensions {
 class Extension;
-class ManifestPermission;
 }
 
 namespace extensions {
 
 // Parses the "event_rules" manifest key.
 class DeclarativeManifestHandler : public ManifestHandler {
  public:
   DeclarativeManifestHandler();
   ~DeclarativeManifestHandler() override;
 
   // ManifestHandler overrides.
   bool Parse(Extension* extension, base::string16* error) override;
 
  private:
   // ManifestHandler overrides.
   const std::vector<std::string> Keys() const override;
 
   DISALLOW_COPY_AND_ASSIGN(DeclarativeManifestHandler);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_API_DECLARATIVE_DECLARATIVE_MANIFEST_HANDLER_H_