Fix a bug in type assertions involving String supertypes.

dart/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,
         super(backend.compiler);
   String get name() => 'SSA code generator';
@@ skipping 2426 matching lines @@
         helper = const SourceString('doubleTypeCheck');
       } else if (element == compiler.numClass) {
         helper = const SourceString('numTypeCheck');
       } else if (element == compiler.boolClass) {
         helper = const SourceString('boolTypeCheck');
       } else if (element == compiler.functionClass || element.isTypedef()) {
         helper = const SourceString('functionTypeCheck');
       } else if (element == compiler.intClass) {
         helper = const SourceString('intTypeCheck');
       } else if (Elements.isStringSupertype(element, compiler)) {
+        additionalArgument = compiler.namer.operatorIs(element);
         if (nativeCheck) {
           helper = const SourceString('stringSuperNativeTypeCheck');
         } else {
           helper = const SourceString('stringSuperTypeCheck');
         }
       } else if (element === compiler.listClass) {
         helper = const SourceString('listTypeCheck');
       } else {
         additionalArgument = compiler.namer.operatorIs(element);
         if (Elements.isListSupertype(element, compiler)) {
@@ skipping 458 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endLabeledBlock(HLabeledBlockInformation labeledBlockInfo) {
     if (labeledBlockInfo.body.start.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }