Accept IPv6 addresses in Uri.http and Uri.https, and correctly nest IPv6 addresses in '[' and ']'.

tests/corelib/uri_ipv4_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.
+
+import 'package:expect/expect.dart';
+
+void testParseIPv4Address() {
+  void pass(String host, List<int> out) {
+    Expect.listEquals(Uri.parseIPv4Address(host), out);
+  }
+  void fail(String host) {
+    Expect.throws(() => Uri.parseIPv4Address(host),
+                  (e) => e is FormatException);
+  }
+
+  pass('127.0.0.1', [127, 0, 0, 1]);
+  pass('128.0.0.1', [128, 0, 0, 1]);
+  pass('255.255.255.255', [255, 255, 255, 255]);
+  pass('0.0.0.0', [0, 0, 0, 0]);
+  fail('127.0.0.-1');
+  fail('255.255.255.256');
+  fail('0.0.0.0.');
+  fail('0.0.0.0.0');
+  fail('a.0.0.0');
+  fail('0.0..0');
+}
+
+void main() {
+  testParseIPv4Address();
+}