Fix misoptimization of 'is' test

runtime/vm/optimizer.h

+// Copyright (c) 2017, 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.
+
+#ifndef RUNTIME_VM_OPTIMIZER_H_
+#define RUNTIME_VM_OPTIMIZER_H_
+
+#include "vm/globals.h"
+
+#include "vm/growable_array.h"
+
+namespace dart {
+
+class Optimizer {
+ public:
+  // Tries to add cid tests to 'results' so that no deoptimization is
+  // necessary for common number-related type tests.  Unconditionally adds an
+  // entry for the Smi type to the start of the array.
+  // TODO(srdjan): Do also for other than numeric types.
+  static bool SpecializeTestCidsForNumericTypes(
+      ZoneGrowableArray<intptr_t>* results,
+      const AbstractType& type);
+};
+
+}  // namespace dart
+
+#endif  // RUNTIME_VM_OPTIMIZER_H_