is__proto__Supported.js

// via me and @kangax
      (function()
      {
        var a = {};
        var someId = new Date();
        var proto = {};
        
        proto[someId] = someId;
        
        return (a.__proto__ = proto, a[someId] === someId) && 
          (a.__proto__ = null, !(a instanceof Object));
      })();