Fix most implementations of UriResolver.restoreAbsolute.

pkg/analyzer/lib/src/generated/source.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.
 
 library engine.source;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 1055 matching lines @@
    * it was resolved, whether or not the resulting source exists, or `null` if it could not be
    * resolved because the URI is invalid.
    *
    * @param uri the URI to be resolved
    * @param actualUri the actual uri for this source -- if `null`, the value of [uri] will be used
    * @return a [Source] representing the file to which given URI was resolved
    */
   Source resolveAbsolute(Uri uri, [Uri actualUri]);
 
   /**
-   * Return an absolute URI that represents the given source, or `null` if a valid URI cannot
-   * be computed.
+   * Return an absolute URI that represents the given [source], or `null` if a
+   * valid URI cannot be computed.
    *
-   * @param source the source to get URI for
-   * @return the absolute URI representing the given source
+   * The computation should be based solely on [source.fullName].
    */
   Uri restoreAbsolute(Source source) => null;
 }