second-argument-null.html worker test is incorrect

[AFBarstow]

This bug was filed as Bugzilla bug 24077. Here is comment #1 but note there are additional comments in the bug:

[[
https://www.w3.org/Bugs/Public/show_bug.cgi?id=24077

The test has:

try {
postMessage(1, null);
} catch(e) {
postMessage(''+e);
}

and asserts that 1 is posted.

But the spec for postMessage is:

void postMessage(any message, optional sequence transfer);

and passing null to the second argument of that should throw, per webidl.

I recommend we do three things:

1. Add a copy of this test that replaces the first postMessage line with:

 postMessage(1);

2. Add a copy of this test that replaces the first postMessage line with:

 postMessage(1, undefined);

3. Modify this test to check that postMessage(1, null) in fact throws.
   Aryeh's submission #1 and Apple's submission #2 would test correct handling of the optional argument when it's not actually passed and Baidu's submission #3 would test correct handling of null here.

]]

[jgraham]

@bzbarsky