Add map() method to List subtype in test.

compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart

Index: compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart
diff --git a/compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart b/compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart
index e64575821b69b89c42266f75c23676bb73805f73..40e6510db2c37d24293eb017d3490acbf33a44d0 100644
--- a/compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart
+++ b/compiler/javatests/com/google/dart/compiler/backend/js/testListSubTypeExprOpt.dart
@@ -22,6 +22,7 @@ class MyList<T> implements List<T> {
   T removeLast() { return null; }
   T last() { return null; }
   void forEach(void f(T)) {}
+  List map(f(T)) { return null; }
   Collection<T> filter(bool f(T)) { return null; }
   bool every(bool f(T)) { return null; }
   bool some(bool f(T)) { return null; }