suggest only superclass elements for "super."

pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart

Index: pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart b/pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart
index 296ca24440c9aa38ae119004c7d55b445cd8420b..0e15afd9f9831b4bdd94f72596b86a2e35a49368 100644
--- a/pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/prefixed_element_contributor.dart
@@ -73,7 +73,8 @@ class _ExpressionSuggestionBuilder implements SuggestionBuilder {
       }
     }
     if (node is Expression) {
-      InterfaceTypeSuggestionBuilder.suggestionsFor(request, node.bestType);
+      InterfaceTypeSuggestionBuilder.suggestionsFor(request, node.bestType,
+          isSuper: node is SuperExpression);
       return new Future.value(true);
     }
     return new Future.value(false);