Use List instead of Link in the type system.

sdk/lib/_internal/compiler/implementation/resolution/scope.dart

Index: sdk/lib/_internal/compiler/implementation/resolution/scope.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/scope.dart b/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
index ebc83d6393cca63ec10e8bff4b047321113e3a7f..79fdacf1115744d3dd45e3794d9d07ea7bced7ce 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
@@ -74,13 +74,11 @@ class TypeDeclarationScope extends NestedScope {
   }
 
   Element lookupTypeVariable(String name) {
-    Link<DartType> typeVariableLink = element.typeVariables;
-    while (!typeVariableLink.isEmpty) {
-      TypeVariableType typeVariable = typeVariableLink.head;
-      if (typeVariable.name == name) {
-        return typeVariable.element;
+    List<DartType> typeVariables = element.typeVariables;
+    for (TypeVariableType type in typeVariables) {
+      if (type.name == name) {
+        return type.element;
       }
-      typeVariableLink = typeVariableLink.tail;
     }
     return null;
   }