[Caja] Changes String(name) to ''+name in Object.prototype.m___ (issue4532074)

[metaweta]

Reviewers: jasvir,

Description:
''+name is faster than String(name) and we already have a gotcha for
it elsewhere.

Please review this at http://codereview.appspot.com/4532074/

Affected files:
  M     src/com/google/caja/es53.js


Index: src/com/google/caja/es53.js
===================================================================
--- src/com/google/caja/es53.js (revision 4476)
+++ src/com/google/caja/es53.js (working copy)
@@ -5156,7 +5156,7 @@
     });

   Object.prototype.m___ = function (name, as) {
-      name = String(name);
+      name = '' + name;
       if (this[name + '_m___']) {
         return this[name].f___(this, as);
       }