Add reverse dns lookup as a method on InternetAddress.

tests/standalone/io/internet_address_test.dart

Index: tests/standalone/io/internet_address_test.dart
diff --git a/tests/standalone/io/internet_address_test.dart b/tests/standalone/io/internet_address_test.dart
index d902ccd9d8fd04a7dcb70ae79358f4db570d7dae..120cacc84e1f718ad9236b2b62cc2494ce2351fc 100644
--- a/tests/standalone/io/internet_address_test.dart
+++ b/tests/standalone/io/internet_address_test.dart
@@ -32,6 +32,21 @@ void testDefaultAddresses() {
   Expect.equals("::", any6.address);
 }
 
+void testReverseLookup() {
+  InternetAddress.lookup('localhost').then((addrs) {
+    addrs.first.reverse().then((addr) {
+      Expect.equals('localhost', addr.host);
+    });
+  });
+
+  InternetAddress.lookup('127.0.0.1').then((addrs) {
+    addrs.first.reverse().then((addr) {
+      Expect.equals('localhost', addr.host);
+    });
+  });
+}
+
 void main() {
   testDefaultAddresses();
+  testReverseLookup();
 }