Add more factory methods to FrontEndStrategy.

pkg/compiler/lib/src/js_backend/runtime_types.dart

Index: pkg/compiler/lib/src/js_backend/runtime_types.dart
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index 03121241365d0d343e5d262ea14be0706230fed3..9482a9e3391a59fbebbd1f51fd9a78e773f9dcb1 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -236,7 +236,7 @@ class _RuntimeTypesNeed implements RuntimeTypesNeed {
   }
 }
 
-class _RuntimeTypesNeedBuilder extends _RuntimeTypesBase
+class RuntimeTypesNeedBuilderImpl extends _RuntimeTypesBase
     implements RuntimeTypesNeedBuilder {
   final Map<ClassElement, Set<ClassElement>> rtiDependencies =
       <ClassElement, Set<ClassElement>>{};