Use List instead of Link in the type system.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of resolution;
 
 abstract class Scope {
   /**
    * Adds [element] to this scope. This operation is only allowed on mutable
    * scopes such as [MethodScope] and [BlockScope].
@@ skipping 56 matching lines @@
   TypeDeclarationScope(parent, this.element)
       : super(parent) {
     assert(parent != null);
   }
 
   Element add(Element newElement) {
     throw "Cannot add element to TypeDeclarationScope";
   }
 
   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;
   }
 
   Element localLookup(String name) => lookupTypeVariable(name);
 
   String toString() =>
       'TypeDeclarationScope($element)';
 }
 
@@ skipping 73 matching lines @@
 
   Element localLookup(String name) => library.find(name);
   Element lookup(String name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element to a library scope";
   }
 
   String toString() => 'LibraryScope($library)';
 }