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

sdk/lib/_internal/dartdoc/test/export_map_test.dart

 // Copyright (c) 2013, 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 'dart:io';
-import 'dart:uri';
 
 import 'package:pathos/path.dart' as pathos;
 import 'package:unittest/unittest.dart';
 
 import '../lib/src/export_map.dart';
 import '../lib/src/dartdoc/utils.dart';
 
 String tempDir;
 
 main() {
@@ skipping 374 matching lines @@
 String libPath(String name) => pathos.normalize(pathos.join(tempDir, name));
 
 void createTempDir() {
   tempDir = new Directory('').createTempSync().path;
   new Directory(pathos.join(tempDir, 'packages')).createSync();
 }
 
 void deleteTempDir() {
   new Directory(tempDir).deleteSync(recursive: true);
 }