Convert a == to a builtin identity check if the receiver type can only hit Object==.

tests/utils/dummy_compiler_test.dart

 // Copyright (c) 2012, 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.
 
 // Smoke test of the dart2js compiler API.
 library dummy_compiler;
 
 import 'dart:async';
 import 'dart:uri';
 
 import '../../sdk/lib/_internal/compiler/compiler.dart';
 
 Future<String> provider(Uri uri) {
   Completer<String> completer = new Completer<String>();
   String source;
   if (uri.scheme == "main") {
     source = "main() {}";
   } else if (uri.scheme == "lib") {
     if (uri.path.endsWith("/core.dart")) {
       source = """library core;
-                  class Object {}
+                  class Object {
+                    operator==(other) {}
+                  }
                   class Type {}
                   class bool {}
                   class num {}
                   class int {}
                   class double{}
                   class String{}
                   class Function{}
                   class List {}
                   class Map {}
                   class Closure {}
@@ skipping 58 matching lines @@
               new Uri.fromComponents(scheme: 'package', path: '/'),
               provider, handler);
   result.then((String code) {
     if (code == null) {
       throw 'Compilation failed';
     }
   }, onError: (AsyncError e) {
       throw 'Compilation failed';
   });
 }