Merge the dart:uri library into dart:core and update the Uri class

sdk/lib/uri/helpers.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.
-
-part of dart.uri;
-
-String merge(String base, String reference) {
-  if (base == "") return "/$reference";
-  return "${base.substring(0, base.lastIndexOf("/") + 1)}$reference";
-}
-
-String removeDotSegments(String path) {
-  List<String> output = [];
-  bool appendSlash = false;
-  for (String segment in path.split("/")) {
-    appendSlash = false;
-    if (segment == "..") {
-      if (!output.isEmpty &&
-          ((output.length != 1) || (output[0] != ""))) output.removeLast();
-      appendSlash = true;
-    } else if ("." == segment) {
-      appendSlash = true;
-    } else {
-      output.add(segment);
-    }
-  }
-  if (appendSlash) output.add("");
-  return output.join("/");
-}