Use List instead of Link in the type system.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index 1615fcfbafbf9537f79816e2ea28d52a944a85c7..78c2f72a1dc4140d540c4fcd32a96f7c30cc5cc4 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -755,7 +755,7 @@ abstract class TypedefElement extends Element
   TypedefType get rawType;
   DartType get alias;
   FunctionSignature get functionSignature;
-  Link<DartType> get typeVariables;
+  List<DartType> get typeVariables;
 
   bool get isResolved;
 
@@ -868,7 +868,7 @@ abstract class TypeDeclarationElement extends Element {
    * available until the type of the element has been computed through
    * [computeType].
    */
-  Link<DartType> get typeVariables;
+  List<DartType> get typeVariables;
 }
 
 abstract class ClassElement extends TypeDeclarationElement
@@ -971,7 +971,7 @@ abstract class ClassElement extends TypeDeclarationElement
 
   void forEachBackendMember(void f(Element member));
 
-  Link<DartType> computeTypeParameters(Compiler compiler);
+  List<DartType> computeTypeParameters(Compiler compiler);
 
   /// Looks up the member [name] in this class.
   Member lookupClassMember(Name name);