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

lib/compiler/implementation/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
   SsaCodeGeneratorTask(JavaScriptBackend backend)
       : this.backend = backend,
@@ skipping 2444 matching lines @@
         helper = backend.getCheckedModeHelper(type);
         if (node.isCastTypeCheck) {
           helper = castNames[helper.stringValue];
         }
       }
       Element helperElement = compiler.findHelper(helper);
       world.registerStaticUse(helperElement);
       List<js.Expression> arguments = <js.Expression>[];
       use(node.checkedInput);
       arguments.add(pop());
-      String additionalArgument = backend.namer.operatorIs(element);
-      arguments.add(new js.LiteralString("'$additionalArgument'"));
+      if (helperElement.computeSignature(compiler).parameterCount != 1) {
+        String additionalArgument = backend.namer.operatorIs(element);
+        arguments.add(new js.LiteralString("'$additionalArgument'"));
+      }
       String helperName = backend.namer.isolateAccess(helperElement);
       push(new js.Call(new js.VariableUse(helperName), arguments));
     } else {
       use(node.checkedInput);
     }
   }
 }
 
 class SsaOptimizedCodeGenerator extends SsaCodeGenerator {
   SsaOptimizedCodeGenerator(backend, work, parameters, parameterNames)
@@ skipping 512 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive() && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }