Use List instead of Link in the type system.

tests/compiler/dart2js/least_upper_bound_test.dart

Index: tests/compiler/dart2js/least_upper_bound_test.dart
diff --git a/tests/compiler/dart2js/least_upper_bound_test.dart b/tests/compiler/dart2js/least_upper_bound_test.dart
index f263f3bed5144afc214d4cd9b9b9b58dbb928c5e..d0976bcf5cde9d0a1de187f32c9f60b3144dfbdd 100644
--- a/tests/compiler/dart2js/least_upper_bound_test.dart
+++ b/tests/compiler/dart2js/least_upper_bound_test.dart
@@ -10,8 +10,6 @@ import 'type_test_helper.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart_types.dart';
 import "../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart"
        show Element, ClassElement;
-import '../../../sdk/lib/_internal/compiler/implementation/util/util.dart'
-       show Link;
 
 void main() {
   testInterface1();
@@ -725,12 +723,12 @@ void testTypeVariable() {
     DartType B = env['B'];
     DartType C = env['C'];
     ClassElement I = env.getElement('I');
-    DartType S = I.typeVariables.head;
-    DartType T = I.typeVariables.tail.head;
-    DartType U = I.typeVariables.tail.tail.head;
-    DartType V = I.typeVariables.tail.tail.tail.head;
-    DartType W = I.typeVariables.tail.tail.tail.tail.head;
-    DartType X = I.typeVariables.tail.tail.tail.tail.tail.head;
+    DartType S = I.typeVariables[0];
+    DartType T = I.typeVariables[1];
+    DartType U = I.typeVariables[2];
+    DartType V = I.typeVariables[3];
+    DartType W = I.typeVariables[4];
+    DartType X = I.typeVariables[5];
 
     checkLub(DartType a, DartType b, DartType expectedLub) {
       DartType lub = env.computeLeastUpperBound(a, b);