DBC: Eager deoptimization and CheckSmi instruction.

tests/language/vm/deopt_smi_check_vm_test.dart

+// Copyright (c) 2016, 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 deoptimization on a smi check.
+// VMOptions=--optimization-counter-threshold=10  --no-background-compilation
+
+import 'package:expect/expect.dart';
+
+hc(a) {
+  var r = a.hashCode;
+  return r;
+}
+
+main() {
+  for (var i = 0; i < 20; i++) {
+    Expect.equals((1).hashCode, hc(1));
+  }
+  // Passing double causes deoptimization.
+  Expect.equals((1.0).hashCode, hc(1.0));
+}