dart2js: Pass type information to constructor rather than add later.

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

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 2bd492d656ede023310ad8c0eaf8463963d25dcb..e813fe938a9f6e0dee1eefc47ca68fd2d6172d24 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -1106,7 +1106,7 @@ class JavaScriptBackend extends Backend {
         type.isFunctionType ? coreTypes.functionType : type;
     if (type is InterfaceType) {
       registry.registerInstantiation(instantiatedType);
-      if (!type.treatAsRaw && classNeedsRti(type.element)) {
+      if (classNeedsRtiField(type.element)) {
         registry.registerStaticUse(new StaticUse.staticInvoke(
             // TODO(johnniwinther): Find the right [CallStructure].
             helpers.setRuntimeTypeInfo,
@@ -1475,8 +1475,14 @@ class JavaScriptBackend extends Backend {
   }
 
   bool classNeedsRti(ClassElement cls) {
-    return rti.classesNeedingRti.contains(cls.declaration) ||
-        compiler.enabledRuntimeType;
+    if (compiler.enabledRuntimeType) return true;
+    return rti.classesNeedingRti.contains(cls.declaration);
+  }
+
+  bool classNeedsRtiField(ClassElement cls) {
+    if (cls.rawType.typeArguments.isEmpty) return false;
+    if (compiler.enabledRuntimeType) return true;
+    return rti.classesNeedingRti.contains(cls.declaration);
   }
 
   bool isComplexNoSuchMethod(FunctionElement element) =>