dart2js load elimination: Look through refinements for locations

tests/compiler/dart2js_native/load_elim_refinement_test.dart

Index: tests/compiler/dart2js_native/load_elim_refinement_test.dart
diff --git a/tests/compiler/dart2js_native/load_elim_refinement_test.dart b/tests/compiler/dart2js_native/load_elim_refinement_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..026b142ac3eab8d90a4118a75522d501466d7a1f
--- /dev/null
+++ b/tests/compiler/dart2js_native/load_elim_refinement_test.dart
@@ -0,0 +1,30 @@
+// 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.
+
+import "package:expect/expect.dart";
+import 'dart:_foreign_helper' show JS;
+
+class A {
+  int a;
+}
+
+class B extends A {
+  int b;
+}
+
+@NoInline()
+escape(v) { g = v; }
+var g;
+
+main() {
+  g = new A();
+  var a = JS('returns:A;new:true', '(1,#)', new B());
+
+  a.a = 1;
+  if (a is B) {
+    escape(a);  // Here we need to escape 'a' not the refinement of a to B.
+    g.a = 2;
+    Expect.equals(2, a.a);
+  }
+}