Remove incorrect ASSERT.

[Mark Lam]

<rdar://problem/83902782>

[Mark Lam]

Created attachment 453178 [details]
proposed patch.

[Keith Miller]

Comment on attachment 453178 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=453178&action=review

> Source/JavaScriptCore/ChangeLog:10
> +        weren't sure that the StringImpl pointer can be null or not.  We're now certain

We should explain why/how the StringImpl can be null.

[Mark Lam]

(In reply to Keith Miller from comment #2)
> Comment on attachment 453178 [details]
> proposed patch.
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=453178&action=review
> 
> > Source/JavaScriptCore/ChangeLog:10
> > +        weren't sure that the StringImpl pointer can be null or not.  We're now certain
> 
> We should explain why/how the StringImpl can be null.

The ASSERT is from here:
```
    auto* impl = string->tryGetValueImpl();
    ASSERT(impl); // FIXME: rdar://83902782
    if (impl && impl->isAtom() && 
        ...
```

... where string is a JSString, which can also be a JSRopeString.

JSString::tryGetValueImpl() is:

```
inline const StringImpl* JSString::tryGetValueImpl() const
{
    uintptr_t pointer = fiberConcurrently();
    if (pointer & isRopeInPointer)
        return nullptr;
    return bitwise_cast<StringImpl*>(pointer);
}
```

Hence, if string is a JSRopeString, the implication can be null.

[Mark Lam]

> Hence, if string is a JSRopeString, the implication can be null.

/implication/impl/ ... sigh auto-correct.

Anyway, I'll add this info to the ChangeLog before landing.

[Mark Lam]

Landed in r290530: <http://trac.webkit.org/r290530>.