Fix math min/max for -0.0 case. Enable min_max_test to run in optimizing compiler as well.

tests/lib/math/min_max_test.dart

Index: tests/lib/math/min_max_test.dart
===================================================================
--- tests/lib/math/min_max_test.dart	(revision 25288)
+++ tests/lib/math/min_max_test.dart	(working copy)
@@ -2,6 +2,7 @@
 // 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.
 // Dart test for testing Math.min and Math.max.
+// VMOptions=--optimization-counter-threshold=10
 
 library min_max_test;
 import "package:expect/expect.dart";
@@ -521,5 +522,7 @@
 
 main() {
   testMin();
+  testMin();
   testMax();
+  testMax();
 }