Clean up TestFeaturesNativeHandler to use the ExtensionsClient's JSON feature sources.

extensions/common/features/feature_provider.h

Index: extensions/common/features/feature_provider.h
diff --git a/extensions/common/features/feature_provider.h b/extensions/common/features/feature_provider.h
index 97f94c65bff71758269d3bda9bb36b69e3cb88a0..887cb22b4ec6f4529186f21a47177bf7f45982f4 100644
--- a/extensions/common/features/feature_provider.h
+++ b/extensions/common/features/feature_provider.h
@@ -31,12 +31,12 @@ class FeatureProvider {
   virtual const std::vector<std::string>& GetAllFeatureNames() const = 0;
 
   // Gets a feature provider for a specific feature type, like "permission".
-  static FeatureProvider* GetByName(const std::string& name);
+  static const FeatureProvider* GetByName(const std::string& name);
 
   // Directly access the common feature types.
-  static FeatureProvider* GetAPIFeatures();
-  static FeatureProvider* GetManifestFeatures();
-  static FeatureProvider* GetPermissionFeatures();
+  static const FeatureProvider* GetAPIFeatures();
+  static const FeatureProvider* GetManifestFeatures();
+  static const FeatureProvider* GetPermissionFeatures();
 };
 
 }  // namespace extensions