Cleanup equality operator to accept any Object rather than just a SourceLocation.

lib/src/location.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 source_span.location;
 
 import 'span.dart';
 
 // A class that describes a single location within a source file.
 class SourceLocation implements Comparable<SourceLocation> {
@@ skipping 59 matching lines @@
   ///
   /// [other] must have the same source URL as [this].
   int compareTo(SourceLocation other) {
     if (sourceUrl != other.sourceUrl) {
       throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
           "\"${other.sourceUrl}\" don't match.");
     }
     return offset - other.offset;
   }
 
-  bool operator ==(SourceLocation other) =>
-      sourceUrl == other.sourceUrl && offset == other.offset;
+  bool operator ==(other) =>
+      other is SourceLocation && sourceUrl == other.sourceUrl &&
+      offset == other.offset;
 
   int get hashCode => sourceUrl.hashCode + offset;
 
   String toString() => '<$runtimeType: $offset $toolString>';
 }