Return -0.. when the input to toStringAs* is -0.0.

frog/leg/lib/js_helper.dart

 // Copyright (c) 2012, 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.
 
 #library('js_helper');
 
 #import('coreimpl.dart');
 
 #source('constant_map.dart');
 #source('date_helper.dart');
@@ skipping 940 matching lines @@
   return receiver < 0 ? receiver.ceil() : receiver.floor();
 }
 
 builtin$toStringAsFixed$1(receiver, fractionDigits) {
   checkNull(receiver);
   if (receiver is !num) {
     return UNINTERCEPTED(receiver.toStringAsFixed(fractionDigits));
   }
   checkNum(fractionDigits);
 
-  return JS('String', @'$0.toFixed($1)', receiver, fractionDigits);
+  String result = JS('String', @'$0.toFixed($1)', receiver, fractionDigits);
+  if (receiver == 0 && receiver.isNegative()) return "-$result";
+  return result;
 }
 
 builtin$toStringAsExponential$1(receiver, fractionDigits) {
   checkNull(receiver);
   if (receiver is !num) {
     return UNINTERCEPTED(receiver.toStringAsExponential(fractionDigits));
   }
   checkNum(fractionDigits);
 
-  return JS('String', @'$0.toExponential($1)', receiver, fractionDigits);
+  String result = JS('String', @'$0.toExponential($1)',
+                     receiver, fractionDigits);
+  if (receiver == 0 && receiver.isNegative()) return "-$result";
+  return result;
 }
 
 builtin$toStringAsPrecision$1(receiver, fractionDigits) {
   checkNull(receiver);
   if (receiver is !num) {
     return UNINTERCEPTED(receiver.toStringAsPrecision(fractionDigits));
   }
   checkNum(fractionDigits);
 
-  return JS('String', @'$0.toPrecision($1)', receiver, fractionDigits);
+  String result = JS('String', @'$0.toPrecision($1)',
+                     receiver, fractionDigits);
+  if (receiver == 0 && receiver.isNegative()) return "-$result";
+  return result;  
 }
 
 builtin$toRadixString$1(receiver, radix) {
   checkNull(receiver);
   if (receiver is !num) {
     return UNINTERCEPTED(receiver.toRadixString(radix));
   }
   checkNum(radix);
 
   return JS('String', @'$0.toString($1)', receiver, radix);
@@ skipping 386 matching lines @@
   String toString() => "Closure";
 }
 
 bool jsHasOwnProperty(var jsObject, String property) {
   return JS('bool', @'$0.hasOwnProperty($1)', jsObject, property);
 }
 
 jsPropertyAccess(var jsObject, String property) {
   return JS('var', @'$0[$1]', jsObject, property);
 }