Fix bug in recompilation handling.

tests/language/field_optimization3_test.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.
+
+// Dart test program to test type-based optimization on fields.
+
+class A {
+  int a = 0;
+  int b = 0;
+  foo() {
+    var c = b + 27;
+    for (var i = 0; i < 1 ; i++) {
+      for (var j = 0; j < 1; j++) {
+        Expect.equals(50, c + 23);
+      }
+    }
+    return a > 0.2;
+  }
+  setA(value) { a = value; }
+  setB(value) { b = value; }
+  operator >(other) => other === 0.2;
+}
+
+main() {
+  var a = new A();
+  Expect.isFalse(a.foo());
+  a.setA(new A());
+  a.setB(0);
+  Expect.isTrue(a.foo());
+}