Fix field-accesses for private fields that were "shadowed" by other private fields.

tests/language/private1.dart

Index: tests/language/private1.dart
diff --git a/tests/language/private1.dart b/tests/language/private1.dart
index 6841cda70451e285a42b4dfacb5508806917210c..62aceb260b07e141469fb2cb8ea362cb445942b2 100644
--- a/tests/language/private1.dart
+++ b/tests/language/private1.dart
@@ -77,8 +77,10 @@ void testPrivateClasses() {
   expectCatch(() => LibOther3.accessFieldB3(b));
 
   C4 c = new C4();
+  Expect.equals(499, c._field1);
   Expect.equals(499, c_field1a(c));
   Expect.equals(499, c.field1a());
+  Expect.equals(42, c._field2);
   Expect.equals(42, c_field2a(c));
   Expect.equals(42, c.field2a());
   Expect.equals(99, LibOther3.c_field1b(c));