Add data-URI support class to dart:core (next to Uri).

tests/lib/uri/uri_http_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";
 
 testHttpUri() {
   void check(Uri uri, String expected) {
     Expect.equals(expected, uri.toString());
   }
@@ skipping 62 matching lines @@
   Uri https = new Uri(scheme: "https");
   Expect.equals("http:$s", http.resolveUri(uri).toString());
   Expect.equals("https:$s", https.resolveUri(uri).toString());
 }
 
 main() {
   testHttpUri();
   testHttpsUri();
   testResolveHttpScheme();
 }