frog: better binding of methods.

tests/language/src/PropertyFieldOverrideTest.dart

+// Copyright (c) 2011, 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.
+
+// Test overriding a getter property with a field.
+class A {
+  abstract int get v();
+
+  int a() {
+    return v - 1;
+  }
+}
+
+class B extends A {
+  int v = 3;
+
+  int b() {
+    return ++v;
+  }
+}
+
+main() {
+  var x = new B();
+  Expect.equals(3, x.v);
+  Expect.equals(2, x.a());
+  Expect.equals(4, x.b());
+}