Enable --harmony-trailing-commas

test/mjsunit/extra-commas.js

 // Copyright 2008 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 20 matching lines @@
     eval(x);
   } catch (e) {
     caught = true;
     assertTrue(e instanceof SyntaxError, "is syntax error");
   }
   assertTrue(caught, "throws exception");
 };
 
 
 assertSyntaxError("f(,)");
-assertSyntaxError("f(1,)");
-assertSyntaxError("f(1,2,)");
+assertSyntaxError("f(1,,)");
+assertSyntaxError("f(1,2,,)");
 
 assertSyntaxError("function f(,) {}");
-assertSyntaxError("function f(1,) {}");
-assertSyntaxError("function f(1,2,) {}");
+assertSyntaxError("function f(1,,) {}");
+assertSyntaxError("function f(1,2,,) {}");