dart2js kernel: generate `other==null` header for operator== methods

pkg/compiler/lib/src/js_backend/backend.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.
 
 library js_backend.backend;
 
 import '../common.dart';
 import '../common/backend_api.dart'
     show ForeignResolver, NativeRegistry, ImpactTransformer;
 import '../common/codegen.dart' show CodegenImpact, CodegenWorkItem;
@@ skipping 688 matching lines @@
   /// Maps compile-time classes to their runtime class.  The runtime class is
   /// always a superclass or the class itself.
   ClassElement getRuntimeClass(ClassElement class_) {
     if (class_.isSubclassOf(commonElements.jsIntClass))
       return commonElements.jsIntClass;
     if (class_.isSubclassOf(commonElements.jsArrayClass))
       return commonElements.jsArrayClass;
     return class_;
   }
 
-  bool operatorEqHandlesNullArgument(FunctionElement operatorEqfunction) {
+  bool operatorEqHandlesNullArgument(FunctionEntity operatorEqfunction) {
     return specialOperatorEqClasses.contains(operatorEqfunction.enclosingClass);
   }
 
   void validateInterceptorImplementsAllObjectMethods(
       ClassEntity interceptorClass) {
     if (interceptorClass == null) return;
     ClassEntity objectClass = commonElements.objectClass;
     compiler.elementEnvironment.forEachClassMember(objectClass,
         (_, MemberEntity member) {
       if (member.isConstructor) return;
@@ skipping 712 matching lines @@
 
   bool canUseAliasedSuperMember(MemberEntity member, Selector selector) {
     return !selector.isGetter;
   }
 
   /// Returns `true` if [member] is called from a subclass via `super`.
   bool isAliasedSuperMember(MemberEntity member) {
     return _aliasedSuperMembers.contains(member);
   }
 }