Don't treat function parameters as let-bound variables in Harmony mode.

test/mjsunit/harmony/block-conflicts.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 112 matching lines @@
   TestConflict('(function (x) { ' + letbinds[l] + '; })()');
 }
 
 // Test conflicting catch/var bindings.
 for (var v = 0; v < varbinds.length; ++v) {
   TestConflict('try {} catch (x) { ' + varbinds[v] + '; }');
 }
 
 // Test conflicting parameter/var bindings.
 for (var v = 0; v < varbinds.length; ++v) {
-  TestConflict('(function (x) { ' + varbinds[v] + '; })()');
+  TestNoConflict('(function (x) { ' + varbinds[v] + '; })()');
 }