Bailout on array optimizations if the array might escape to reflection land.

tests/compiler/dart2js/array_tracing_mirror_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.
+
+// Make sure that limiting mirrors through @MirrorsUsed does not
+// affect optimizations done on arrays.
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+import 'memory_compiler.dart';
+
+const MEMORY_SOURCE_FILES = const {
+  'main.dart': '''
+
+@MirrorsUsed(targets: 'main')
+import 'dart:mirrors';
+class A {
+  var field;
+}
+
+main() {
+  var a = new A();
+  var mirror = reflect(a);
+  var array = [42, 42];
+  a.field = array;
+  var field = mirror.getField(#field);
+  field.invoke(#clear, []);
+  return array.length;
+}
+''',
+};
+
+main() {
+  var compiler = compilerFor(MEMORY_SOURCE_FILES);  
+  asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    var element = compiler.mainApp.findExported('main');
+    var code = compiler.backend.assembleCode(element);
+    Expect.isTrue(code.contains('return 2'));
+  }));
+}
+