[debugger] do not expose temporary variables introduced by the parser.

test/mjsunit/es6/debug-blockscopes.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 130 matching lines @@
     }
     count++;
   }
 
   // 'arguments' and might be exposed in the local and closure scope. Just
   // ignore this.
   var scope_size = scope.scopeObject().properties().length;
   if (!scope.scopeObject().property('arguments').isUndefined()) {
     scope_size--;
   }
-  // Skip property with empty name.
-  if (!scope.scopeObject().property('').isUndefined()) {
-    scope_size--;
-  }
+  // Temporary variables introduced by the parser have not been materialized.
+  assertTrue(scope.scopeObject().property('').isUndefined());
 
   if (count != scope_size) {
     print('Names found in scope:');
     var names = scope.scopeObject().propertyNames();
     for (var i = 0; i < names.length; i++) {
       print(names[i]);
     }
   }
   assertEquals(count, scope_size);
 
@@ skipping 367 matching lines @@
     debugger;
   }
 }
 
 listener_delegate = function (exec_state) {
   assertEqualsUnlessOptimized(0, exec_state.frame(0).evaluate("i").value());
   assertEqualsUnlessOptimized(5, exec_state.frame(0).evaluate("j").value());
 }
 shadowing_2();
 EndTest();