Move div by zero testing into its own test.

tests/language/div_with_power_of_two_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 division by power of two.
 // Test that results before and after optimization are the same.
 // VMOptions=--optimization-counter-threshold=10 --no-use-osr
 
 import "package:expect/expect.dart";
 
 // [function, [list of tuples argument/result]].
@@ skipping 80 matching lines @@
   for (int i = 0; i < 20; i++) {
     for (var e in expectedResults) {
       Function f = e[0];
       List values = e[1];
       for (var v in values) {
         int arg = v[0];
         int res = v[1];
         Expect.equals(res, f(arg));
       }
     }
-    Expect.throws(() => divBy0(4),
-                  (e) => e is IntegerDivisionByZeroException
-                         || e is UnsupportedError);
   }
 }