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

tests/lib/uri/uri_parse_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 testUriCombi() {
   var schemes = ["", "file", "ws", "ftp"];
   var fragments = ["", "#", "#f", "#fragment", "#l:?/"];
@@ skipping 52 matching lines @@
           }
         }
       }
     }
   }
 }
 
 void main() {
   testUriCombi();
 }