Make sure TypeErrors thrown by frozen are caught

lib/chai/core/assertions.js

@@ -1719,11 +1719,24 @@ module.exports = function (chai, _) {
   Assertion.addProperty('frozen', function() {
     var obj = flag(this, 'object');
 
+    // In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError.
+    // In ES6, a non-object argument will be treated as if it was a frozen ordinary object, simply return true.
+    // See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isFrozen
+    // The following provides ES6 behavior when a TypeError is thrown under ES5.
+
+    var isFrozen;
+
+    try {
+      isFrozen = Object.isFrozen(obj);
+    } catch (err) {
+      if (err instanceof TypeError) isFrozen = true;
+      else throw err;
+    }
+
     this.assert(
-      Object.isFrozen(obj)
+      isFrozen
       , 'expected #{this} to be frozen'
       , 'expected #{this} to not be frozen'
     );
   });
-
 };