dart2js: Always generate functions for rti substitutions.

pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart
index 273984bcfe79b0c775fd43eb5d1f4879060a6292..a8bd2eb6c55f7ca873cc42b9fd97aa15edd9d635 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/type_test_emitter.dart
@@ -55,8 +55,7 @@ class TypeTestEmitter extends CodeEmitterHelper {
       RuntimeTypes rti = backend.rti;
       jsAst.Expression expression;
       bool needsNativeCheck = emitter.nativeEmitter.requiresNativeIsCheck(cls);
-      expression = rti.getSupertypeSubstitution(
-          classElement, cls, alwaysGenerateFunction: true);
+      expression = rti.getSupertypeSubstitution(classElement, cls);
       if (expression == null && (emitNull || needsNativeCheck)) {
         expression = new jsAst.LiteralNull();
       }
@@ -220,7 +219,7 @@ class TypeTestEmitter extends CodeEmitterHelper {
         properties.add([namer.operatorIs(checkedClass), js('TRUE')]);
         Substitution substitution = check.substitution;
         if (substitution != null) {
-          jsAst.Expression body = substitution.getCode(rti, false);
+          jsAst.Expression body = substitution.getCode(rti);
           properties.add([namer.substitutionName(checkedClass), body]);
         }
       }