Fix test to use developer mode. DartC does not have to check arguments to native methods.

tests/language/src/MathVMTest.dart

Index: tests/language/src/MathVMTest.dart
===================================================================
--- tests/language/src/MathVMTest.dart	(revision 505)
+++ tests/language/src/MathVMTest.dart	(working copy)
@@ -1,9 +1,7 @@
 // Copyright (c) 2011, 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.
-// Tests weird cornercases of class Math.
-// An exception is thrown either by the type checker (development mode) or by
-// library (default mode).
+// Tests that the VM does not crash on weird cornercases of class Math.
 
 class FakeNumber {
   const FakeNumber();