Consolidate duplicate code for resloving URIs.

pkg/analyzer/lib/file_system/memory_file_system.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 analyzer.file_system.memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 
@@ skipping 438 matching lines @@
 
   @override
   bool operator ==(other) {
     return other is _MemoryFileSource && other.id == id;
   }
 
   @override
   bool exists() => file.exists;
 
   @override
-  Uri resolveRelativeUri(Uri relativeUri) {
-    Uri baseUri = uri;
-    String scheme = uri.scheme;
-    if (scheme == DartUriResolver.DART_SCHEME) {
-      String libraryName = uri.path;
-      baseUri = Uri.parse('$scheme:$libraryName/$libraryName.dart');
-    }
-    return baseUri.resolveUri(relativeUri);
-  }
-
-  @override
   String toString() => file.toString();
 }
 
 /**
  * An in-memory implementation of [Folder].
  */
 class _MemoryFolder extends _MemoryResource implements Folder {
   _MemoryFolder(MemoryResourceProvider provider, String path)
       : super(provider, path);
 
@@ skipping 101 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }