All strong mode cleaning of dart2js.

tests/compiler/dart2js/mixin_typevariable_test.dart

Index: tests/compiler/dart2js/mixin_typevariable_test.dart
diff --git a/tests/compiler/dart2js/mixin_typevariable_test.dart b/tests/compiler/dart2js/mixin_typevariable_test.dart
index deb26abc83d8d1d6999d9a3b7c3fa21637d9cac0..ec29f2050c9a28964958f557e69899c095df976a 100644
--- a/tests/compiler/dart2js/mixin_typevariable_test.dart
+++ b/tests/compiler/dart2js/mixin_typevariable_test.dart
@@ -8,7 +8,7 @@ import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'type_test_helper.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
-import "package:compiler/src/elements/elements.dart" show Element, ClassElement;
+import "package:compiler/src/elements/elements.dart" show ClassElement;
 
 void main() {
   testMixinSupertypes();
@@ -33,7 +33,6 @@ void testMixinSupertypes() {
         ClassElement S = env.getElement('S');
         ClassElement M1 = env.getElement('M1');
         ClassElement M2 = env.getElement('M2');
-        ClassElement M3 = env.getElement('M3');
         ClassElement C1 = env.getElement('C1');
         ClassElement C2 = env.getElement('C2');
 
@@ -112,11 +111,6 @@ void testNonTrivialSubstitutions() {
         ClassElement F1 = env.getElement('F1');
         ClassElement F2 = env.getElement('F2');
 
-        ClassElement C1_A_B = C1.superclass;
-        ClassElement D1_A_B = D1.superclass;
-        ClassElement E1_A_B = E1.superclass;
-        ClassElement F1_A_B = F1.superclass;
-
         void testSupertypes(ClassElement element,
             Map<ClassElement, List<ResolutionDartType>> typeArguments) {
           if (element != Object) {