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

chrome/browser/bookmarks/enhanced_bookmarks_features.cc

Index: chrome/browser/bookmarks/enhanced_bookmarks_features.cc
diff --git a/chrome/browser/bookmarks/enhanced_bookmarks_features.cc b/chrome/browser/bookmarks/enhanced_bookmarks_features.cc
index e18f18f7dbe637a817560ef643d0c8dd6d4e1176..3b9cfb05feb9d984a84c7cd4fe4a8abd8609e111 100644
--- a/chrome/browser/bookmarks/enhanced_bookmarks_features.cc
+++ b/chrome/browser/bookmarks/enhanced_bookmarks_features.cc
@@ -54,7 +54,7 @@ bool IsEnhancedBookmarksExperimentEnabled() {
   }
 
   std::string ext_id = GetEnhancedBookmarksExtensionIdFromFinch();
-  extensions::FeatureProvider* feature_provider =
+  const extensions::FeatureProvider* feature_provider =
       extensions::FeatureProvider::GetPermissionFeatures();
   extensions::Feature* feature = feature_provider->GetFeature("metricsPrivate");
   return feature && feature->IsIdInWhitelist(ext_id);