Implement SearchEngine.searchAllSubtypes() with the analysis driver.

pkg/analysis_server/lib/src/services/search/hierarchy.dart

Index: pkg/analysis_server/lib/src/services/search/hierarchy.dart
diff --git a/pkg/analysis_server/lib/src/services/search/hierarchy.dart b/pkg/analysis_server/lib/src/services/search/hierarchy.dart
index 1822f1baa0861eae73972438a53c541d3906cf6c..92aca414d17db2fc2c19082bd9b40f35da9f54c3 100644
--- a/pkg/analysis_server/lib/src/services/search/hierarchy.dart
+++ b/pkg/analysis_server/lib/src/services/search/hierarchy.dart
@@ -87,7 +87,7 @@ Future<Set<ClassMemberElement>> getHierarchyMembers(
     }
     // check all sub- classes
     Set<ClassElement> subClasses =
-        await getSubClasses(searchEngine, superClass);
+        await searchEngine.searchAllSubtypes(superClass);
     subClasses.add(superClass);
     for (ClassElement subClass in subClasses) {
       List<Element> subClassMembers = getChildren(subClass, name);
@@ -119,15 +119,6 @@ List<Element> getMembers(ClassElement clazz) {
 }
 
 /**
- * Returns a [Set] with all direct and indirect subclasses of [seed].
- */
-Future<Set<ClassElement>> getSubClasses(
-    SearchEngine searchEngine, ClassElement seed) async {
-  List<SearchMatch> matches = await searchEngine.searchAllSubtypes(seed);
-  return matches.map((match) => match.element).toSet();
-}
-
-/**
  * Returns a [Set] with all direct and indirect superclasses of [seed].
  */
 Set<ClassElement> getSuperClasses(ClassElement seed) {