dart2js cps: Do not inline string interpolation helper.

pkg/compiler/lib/src/cps_ir/inline.dart

 // Copyright (c) 2015, 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 cps_ir.optimization.inline;
 
 import 'cps_fragment.dart';
 import 'cps_ir_builder.dart' show ThisParameterLocal;
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
@@ skipping 580 matching lines @@
 
   bool isBlacklisted(FunctionElement target) {
     ClassElement enclosingClass = target.enclosingClass;
     if (target.isOperator &&
         (enclosingClass == backend.helpers.jsNumberClass ||
          enclosingClass == backend.helpers.jsDoubleClass ||
          enclosingClass == backend.helpers.jsIntClass)) {
       // These should be handled by operator specialization.
       return true;
     }
+    if (target == backend.helpers.stringInterpolationHelper) return true;
     return false;
   }
 }