Do not pass the name of the is check if it's not required (typically for primitive types).

lib/compiler/implementation/js_backend/emitter.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.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 520 matching lines @@
     DartType type = member.computeType(compiler);
     if (type.element.isTypeVariable()
         || type.element == compiler.dynamicClass
         || type.element == compiler.objectClass) {
       // TODO(ngeoffray): Support type checks on type parameters.
       return null;
     } else {
       SourceString helper = compiler.backend.getCheckedModeHelper(type);
       Element helperElement = compiler.findHelper(helper);
       String helperName = namer.isolateAccess(helperElement);
-      String additionalArgument = namer.operatorIs(type.element);
+      String additionalArgument = '';
+      if (helperElement.computeSignature(compiler).parameterCount != 1) {
+        additionalArgument = ", '${namer.operatorIs(type.element)}'";
+      }
       return " set\$$fieldName: function(v) { "
-          "this.$fieldName = $helperName(v, '$additionalArgument'); }";
+          "this.$fieldName = $helperName(v$additionalArgument); }";
     }
   }
 
   List<String> emitClassFields(ClassElement classElement, CodeBuffer buffer) {
     // If the class is never instantiated we still need to set it up for
     // inheritance purposes, but we can simplify its JavaScript constructor.
     bool isInstantiated =
         compiler.codegenWorld.instantiatedClasses.contains(classElement);
     List<String> checkedSetters = <String>[];
 
@@ skipping 823 matching lines @@
 const String HOOKS_API_USAGE = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;