Promote Stephen's InterfaceInheritFieldTest to a language test.

tests/language/src/SuperFieldAccessTest.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.
+
+class A {
+  int foo;
+  A(this.foo);
+
+  raw$foo() => foo;
+  this$foo() => this.foo;
+}
+
+class B extends A {
+  int foo;
+  B.b1(x, this.foo) : super(x);
+  B.b2(x, y) : this.foo = y, super(x);
+  B.b3(x, y) : super(x), this.foo = y;  
+
+  super$foo() => super.foo;
+  sum() => foo + super.foo;
+}
+
+test(b) {
+  Expect.equals(10, b.foo);
+  Expect.equals(10, b.raw$foo());
+  Expect.equals(10, b.this$foo());  
+  Expect.equals(100, b.super$foo());
+  Expect.equals(110, b.sum());
+}
+
+main() {
+  test(new B.b1(100, 10));
+  test(new B.b2(100, 10));
+  test(new B.b3(100, 10));  
+}