Wrap harmony implementations in functions.

src/harmony-tostring.js

Index: src/harmony-tostring.js
diff --git a/src/harmony-tostring.js b/src/harmony-tostring.js
index 89a314c5081e10a5c84512a058921a947e80a29b..1ecfb263935bf98025645afc679f35d15a88c4a0 100644
--- a/src/harmony-tostring.js
+++ b/src/harmony-tostring.js
@@ -2,15 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+(function() {
+
 "use strict";
 
-function HarmonyToStringExtendSymbolPrototype() {
-  %CheckIsBootstrapping();
+%CheckIsBootstrapping();
+
+var GlobalSymbol = global.Symbol;
 
-  InstallConstants(global.Symbol, [
-     // TODO(dslomov, caitp): Move to symbol.js when shipping
-     "toStringTag", symbolToStringTag
-  ]);
-}
+InstallConstants(GlobalSymbol, [
+   // TODO(dslomov, caitp): Move to symbol.js when shipping
+   "toStringTag", symbolToStringTag
+]);
 
-HarmonyToStringExtendSymbolPrototype();
+})();