Request.constructor misses checking for the type of init.signal param

[[e-mail]]

Steps to reproduce:

(1) Open a tab and navigate to any URL;
(2) Run the following code in the Console of Devtools:
```
new Request('', {signal:{}})
```
(3) Then this code would be evaluated successfully without throwing any exception. Only a warning is asserted.

Actual results:

This code would be evaluated successfully without throwing any exception. Only a warning is asserted.

Expected results:

As https://fetch.spec.whatwg.org/#requestinfo says, the init.signal param is of AbortSignal type. Since the code above sets the input param as {}, a TypeError exception should be thrown. (Just behave as what the warning says.)

BTW, in my test both Chrome and Firefox throw exceptions when evaluating this code.

[youenn fablet]

See https://bugs.webkit.org/show_bug.cgi?id=199576 for some background info on why it is difficult to make it throw.
@zyscoder, what is the impact of not throwing here for you?

[Radar WebKit Bug Importer]

<rdar://problem/79140275>