Do not do global optimizations on fields and parameters when invokeOn is enabled.

tests/compiler/dart2js_extra/inference_nsm_mirrors_test.dart

+// Copyright (c) 2013, 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.
+
+// Regression test for dart2js that did type inferencing on parameters
+// whose type may change at runtime due to an invocation through
+// [InstanceMirror.delegate].
+
+@MirrorsUsed(targets: 'A')
+import 'dart:mirrors';
+import 'package:expect/expect.dart';
+
+class A {
+  noSuchMethod(im) {
+    reflect(new B()).delegate(im);
+  }
+}
+
+class B {
+  foo(a) => a + 42;
+}
+
+main() {
+  Expect.equals(42, new B().foo(0));
+  Expect.throws(() => new A().foo('foo'), (e) => e is UnsupportedError);
+}