Fix floating point issues on Windows.

runtime/lib/math.cc

 // 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.
 
 #include <ctype.h>  // isspace.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/exceptions.h"
@@ skipping 35 matching lines @@
 }
 
 DEFINE_NATIVE_ENTRY(Math_atan, 1) {
   GET_NATIVE_ARGUMENT(Double, operand, arguments->NativeArgAt(0));
   return Double::New(atan(operand.value()));
 }
 
 DEFINE_NATIVE_ENTRY(Math_atan2, 2) {
   GET_NATIVE_ARGUMENT(Double, operand1, arguments->NativeArgAt(0));
   GET_NATIVE_ARGUMENT(Double, operand2, arguments->NativeArgAt(1));
-  return Double::New(atan2(operand1.value(), operand2.value()));
+  return Double::New(atan2_ieee(operand1.value(), operand2.value()));
 }
 
 DEFINE_NATIVE_ENTRY(Math_exp, 1) {
   GET_NATIVE_ARGUMENT(Double, operand, arguments->NativeArgAt(0));
   return Double::New(exp(operand.value()));
 }
 
 DEFINE_NATIVE_ENTRY(Math_log, 1) {
   GET_NATIVE_ARGUMENT(Double, operand, arguments->NativeArgAt(0));
   return Double::New(log(operand.value()));
 }
 
 }  // namespace dart