Disable hoisting of checked-mode assertions out of loops.

tests/language/optimized_hoisting_checked_mode_assert.dart

+// 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.
+
+// Test checked mode assertions inside loops.
+
+int foo(x, n)  {
+  double z = 0.0;
+  for (var i=0; i<n; i++) {
+    double z = x;
+  }
+  return 0;
+}
+
+main() {
+  for (var i=0; i<10000; i++) foo(1.0, 10);
+  Expect.equals(0, foo(1.0, 10));
+  Expect.equals(0, foo(2, 0));  // Must not throw in checked mode.
+}
+