Revert r23330 and r23136 because of a bug with loop invariant code motion.

tests/language/licm3_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.
+
+// Test that a loop invariant code motion optimization correctly hoists
+// instructions that may cause deoptimization.
+
+import "package:expect/expect.dart";
+
+foo(o) {
+  var r = 0;
+  for (var i = 0; i < 3; i++) {
+    r += o.z;
+  }
+  return r;
+}
+
+
+class A {
+  var z = 3;
+}
+
+main() {
+  var a = new A();
+  for(var i = 0; i < 10000; i++) foo(a);
+  Expect.equals(9, foo(a));
+  Expect.throws(() => foo(42));
+  for(var i = 0; i < 10000; i++) foo(a);
+  Expect.throws(() => foo(42));
+}
+