dart2js: Fix checked mode error in nameForGetOneShotInterceptor.

pkg/compiler/lib/src/js_backend/minify_namer.dart

 // Copyright (c) 2011, 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.
 
 part of js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class MinifyNamer extends Namer with _MinifiedFieldNamer,
@@ skipping 325 matching lines @@
   @override
   jsAst.Name nameForGetOneShotInterceptor(Selector selector,
       Iterable<ClassElement> classes) {
     String root = selector.isOperator
         ? operatorNameToIdentifier(selector.name)
         : privateName(selector.memberName);
     String prefix = selector.isGetter
         ? r"$get"
         : selector.isSetter ? r"$set" : "";
     String callSuffix =
-        selector.isCall ? callSuffixForStructure(selector.callStructure) : "";
+        selector.isCall ? callSuffixForStructure(selector.callStructure).join()
+                        : "";
     String suffix = suffixForGetInterceptor(classes);
     String fullName = "\$intercepted$prefix\$$root$callSuffix\$$suffix";
     return _disambiguateInternalGlobal(fullName);
   }
 }