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

pkg/stack_trace/lib/src/utils.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.
 
 library utils;
 
 import 'dart:io';
-import 'dart:uri';
 
 import 'package:pathos/path.dart' as path;
 
 /// Converts a `file:` [Uri] to a local path string.
 String fileUriToPath(Uri uri) {
   if (uri.scheme != 'file') {
     throw new ArgumentError("Uri $uri must have scheme 'file:'.");
   }
   if (Platform.operatingSystem != 'windows') return uri.path;
   if (uri.path.startsWith("/")) {
@@ skipping 12 matching lines @@
   if (Platform.operatingSystem != 'windows') {
     return Uri.parse('file://$pathString');
   } else if (path.rootPrefix(pathString).startsWith('\\\\')) {
     // Network paths become "file://hostname/path/to/file".
     return Uri.parse('file:${pathString.replaceAll("\\", "/")}');
   } else {
     // Drive-letter paths become "file:///C:/path/to/file".
     return Uri.parse('file:///${pathString.replaceAll("\\", "/")}');
   }
 }