Package map source factory support [FIXED].

pkg/analyzer/lib/src/generated/utilities_dart.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.utilities.dart;
 
 import 'java_core.dart';
@@ skipping 20 matching lines @@
   final bool isOptional;
 
   /**
    * Initialize a newly created kind with the given state.
    *
    * @param isOptional `true` if this is an optional parameter
    */
   const ParameterKind(String name, int ordinal, this.isOptional)
       : super(name, ordinal);
 }
+
+/**
+ * Check whether [uri1] starts with (or 'is prefixed by') [uri2] by checking
+ * path segments.
+ */
+bool startsWith(Uri uri1, Uri uri2) {
+  List<String> uri1Segments = uri1.pathSegments;
+  List<String> uri2Segments = uri2.pathSegments.toList();
+  // Trim trailing empty segments ('/foo/' => ['foo', ''])
+  if (uri2Segments.last == '') {
+    uri2Segments.removeLast();
+  }
+
+  if (uri2Segments.length > uri1Segments.length) {
+    return false;
+  }
+
+  for (int i = 0; i < uri2Segments.length; ++i) {
+    if (uri2Segments[i] != uri1Segments[i]) {
+      return false;
+    }
+  }
+  return true;
+}