[Extensions] Break up BaseFeatureProvider, create JSONFeatureProvider

extensions/common/features/base_feature_provider.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_BASE_FEATURE_PROVIDER_H_
 #define EXTENSIONS_COMMON_FEATURES_BASE_FEATURE_PROVIDER_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
+#include "base/macros.h"
 #include "extensions/common/features/feature_provider.h"
-#include "extensions/common/features/simple_feature.h"
-
-namespace Base {
-class DictionaryValue;
-}
 
 namespace extensions {
+class Feature;
 
-// Reads Features out of a simple JSON file description.
+// A FeatureProvider contains the mapping of all feature names specified in the
+// _*_features.json files to the Feature classes. Look up a Feature by its name
+// to determine whether or not it is available in a certain context.
+// Subclasses implement the specific logic for how the features are populated;
+// this class handles vending the features given the query.
+// TODO(devlin): We could probably combine this and FeatureProvider, since both
+// contain common functionality and neither are designed to be full
+// implementations.
 class BaseFeatureProvider : public FeatureProvider {
  public:
-  typedef SimpleFeature*(*FeatureFactory)();
-
-  // Creates a new BaseFeatureProvider. Pass null to |factory| to have the
-  // provider create plain old Feature instances.
-  BaseFeatureProvider(const base::DictionaryValue& root,
-                      FeatureFactory factory);
   ~BaseFeatureProvider() override;
 
   // Gets the feature |feature_name|, if it exists.
   Feature* GetFeature(const std::string& feature_name) const override;
   Feature* GetParent(Feature* feature) const override;
   std::vector<Feature*> GetChildren(const Feature& parent) const override;
 
   const FeatureMap& GetAllFeatures() const override;
 
- private:
+ protected:
+  BaseFeatureProvider();
   std::map<std::string, std::unique_ptr<Feature>> features_;
 
-  // Populated on first use.
-  mutable std::vector<std::string> feature_names_;
-
-  FeatureFactory factory_;
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BaseFeatureProvider);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_BASE_FEATURE_PROVIDER_H_