Consolidate duplicate code for resloving URIs.

pkg/analyzer/lib/src/context/source.dart

 // Copyright (c) 2015, 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 analyzer.src.context.source;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 268 matching lines @@
    * @throws AnalysisException if either the contained URI is invalid or if it
    *         cannot be resolved against the source object's URI
    */
   Source _internalResolveUri(Source containingSource, Uri containedUri) {
     if (!containedUri.isAbsolute) {
       if (containingSource == null) {
         throw new AnalysisException(
             "Cannot resolve a relative URI without a containing source: "
             "$containedUri");
       }
-      containedUri = containingSource.resolveRelativeUri(containedUri);
+      containedUri = utils.resolveRelativeUri(containingSource.uri, containedUri);
     }
 
     Uri actualUri = containedUri;
 
     // Check .packages and update target and actual URIs as appropriate.
     if (_packages != null && containedUri.scheme == 'package') {
       Uri packageUri = null;
       try {
         packageUri =
             _packages.resolve(containedUri, notFound: (Uri packageUri) => null);
@@ skipping 13 matching lines @@
     for (UriResolver resolver in resolvers) {
       Source result = resolver.resolveAbsolute(containedUri, actualUri);
       if (result != null) {
         return result;
       }
     }
 
     return null;
   }
 }