Support percent/permille formats with positive and negative variations

pkg/intl/test/number_format_test.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 number_format_test;
 
 import 'package:unittest/unittest.dart';
 import 'package:intl/number_symbols_data.dart';
@@ skipping 169 matching lines @@
     // Verify that we can pass null in order to specify the currency symbol
     // but use the default locale.
     var defaultLocale = new NumberFormat.currencyPattern(null, 'Smurfs');
     formatted = defaultLocale.format(amount);
     // We don't know what the exact format will be, but it should have Smurfs.
     expect(formatted.contains('Smurfs'), isTrue);
     readBack = defaultLocale.parse(formatted);
     expect(readBack, amount);
   });
 
+  test("Delta percent format", () {
+    var f = new NumberFormat("+#,##0%;-#,##0%");
+    expect(f.format(-0.07), "-7%");
+    expect(f.format(0.12), "+12%");
+  });
+
   test('Unparseable', () {
     var format = new NumberFormat.currencyPattern();
     expect(() => format.parse("abcdefg"), throwsFormatException);
     expect(() => format.parse(""), throwsFormatException);
     expect(() => format.parse("1.0zzz"), throwsFormatException);
     expect(() => format.parse("-∞+1"), throwsFormatException);
   });
 }