[Extensions] Add a SimpleFeature::Validate function

extensions/common/features/api_feature.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 EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_
 #define EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_
 
 #include <string>
 
 #include "extensions/common/features/simple_feature.h"
 
 namespace extensions {
 
 class APIFeature : public SimpleFeature {
  public:
   APIFeature();
   ~APIFeature() override;
 
   // extensions::Feature:
-  bool IsInternal() const override;
-
-  std::string Parse(const base::DictionaryValue* value) override;
-
- private:
-  bool internal_;
+  bool Validate(std::string* error) override;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_