Warn about overriding operator== but not hashCode.

dart/tests/compiler/dart2js/mirror_tree_shaking_test.dart

 // Copyright (c) 2013, 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.
 
 // Test that tree-shaking hasn't been turned off.
 
 import 'package:expect/expect.dart';
 import 'memory_source_file_helper.dart';
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
        show NullSink;
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart'
        show Diagnostic;
 
 import 'dart:async';
 
 main() {
   Uri script = currentDirectory.resolve(nativeToUriPath(Platform.script));
   Uri libraryRoot = script.resolve('../../../sdk/');
   Uri packageRoot = script.resolve('./packages/');
 
   MemorySourceFileProvider.MEMORY_SOURCE_FILES = MEMORY_SOURCE_FILES;
   var provider = new MemorySourceFileProvider();
   void diagnosticHandler(Uri uri, int begin, int end,
                          String message, Diagnostic kind) {
-    if (kind == Diagnostic.VERBOSE_INFO || kind == Diagnostic.WARNING) {
+    if (kind == Diagnostic.VERBOSE_INFO
+        || kind == Diagnostic.WARNING
+        || kind == Diagnostic.HINT) {
       return;
     }
     throw '$uri:$begin:$end:$message:$kind';
   }
 
   EventSink<String> outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 
   Compiler compiler = new Compiler(provider.readStringFromUri,
@@ skipping 18 matching lines @@
     print('Invoked ${MirrorSystem.getName(invocation.memberName)}');
     return reflect('foobar').delegate(invocation);
   }
 }
 
 void main() {
   print(new Foo().substring(3));
 }
 """,
 };