Fix equality between subclasses of Source

pkg/analyzer/lib/src/generated/source_io.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.src.generated.source_io;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_core.dart';
@@ skipping 221 matching lines @@
   @override
   String get shortName => file.getName();
 
   @override
   UriKind get uriKind {
     String scheme = uri.scheme;
     return UriKind.fromScheme(scheme);
   }
 
   @override
-  bool operator ==(Object object) =>
-      object is FileBasedSource && id == object.id;
+  bool operator ==(Object object) {
+    if (object is FileBasedSource) {
+      return id == object.id;
+    } else if (object is Source) {
+      return uri == object.uri;
+    }
+    return false;
+  }
 
   @override
   bool exists() => file.isFile();
 
   @override
   String toString() {
     if (file == null) {
       return "<unknown source>";
     }
     return file.getAbsolutePath();
@@ skipping 297 matching lines @@
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `file` URI
    */
   static bool isFileUri(Uri uri) => uri.scheme == FILE_SCHEME;
 }