Do not track parameter types of closures, since closure calls can be generated during the emitter.

tests/language/closure_parameter_types_test.dart

Index: tests/language/closure_parameter_types_test.dart
===================================================================
--- tests/language/closure_parameter_types_test.dart	(revision 0)
+++ tests/language/closure_parameter_types_test.dart	(revision 0)
@@ -0,0 +1,24 @@
+// 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.
+
+// Regression test for dart2js, where the optimizer was too agressive
+// about parameter types of closures.
+
+class A {
+  Function f;
+  A(this.f);
+  _do() => f(1);
+}
+
+main() {
+  int invokeCount = 0;
+  closure(a) {
+    if (invokeCount++ == 1) {
+      Expect.isTrue(a is int);
+    }
+  }
+  closure('s');
+  new A(closure)._do();
+  Expect.equals(2, invokeCount);
+}