[Extensions] Break up BaseFeatureProvider, create JSONFeatureProvider

extensions/common/features/base_feature_provider.h

Index: extensions/common/features/base_feature_provider.h
diff --git a/extensions/common/features/base_feature_provider.h b/extensions/common/features/base_feature_provider.h
index 503371e05862518348487d5ece77d6be387e157e..59c16699d591324619808db6c8b919164b33ee95 100644
--- a/extensions/common/features/base_feature_provider.h
+++ b/extensions/common/features/base_feature_provider.h
@@ -10,24 +10,22 @@
 #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 {
-
-// Reads Features out of a simple JSON file description.
+class Feature;
+
+// 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.
@@ -37,13 +35,12 @@ class BaseFeatureProvider : public FeatureProvider {
 
   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