Convert to async/await parts that cause strong mode warnings.

pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart

Index: pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
diff --git a/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart b/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
index 5450e60b15a0b449f248ba5888a821196d7b57a4..5cd0820c4b5c5e9bcdf9774a818f609b4598587c 100644
--- a/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
+++ b/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
@@ -262,18 +262,15 @@ class Pivot /* target */ extends Base2 {}
     return Future.forEach(tests, (test) => test());
   }
 
-  Future<HierarchyResults> typeHierarchyTest(String text) {
+  Future<HierarchyResults> typeHierarchyTest(String text) async {
     int offset = text.indexOf(' /* target */') - 1;
     sendAnalysisUpdateContent({pathname: new AddContentOverlay(text)});
-    return analysisFinished
-        .then((_) => sendSearchGetTypeHierarchy(pathname, offset))
-        .then((result) {
-      if (result.hierarchyItems == null) {
-        return null;
-      } else {
-        return new HierarchyResults(
-            result.hierarchyItems as List<TypeHierarchyItem>);
-      }
-    });
+    await analysisFinished;
+    var result = await sendSearchGetTypeHierarchy(pathname, offset);
+    if (result.hierarchyItems == null) {
+      return null;
+    } else {
+      return new HierarchyResults(result.hierarchyItems);
+    }
   }
 }