fix IE11 Script Access Denied error.

[doctyper]

This pull request fixes an issue that surfaced when we used core-js on a page containing iframes in IE11. Attempting to access properties on the iframe threw Script Access Denied errors.

[doctyper]

The fix here was to add the TAG in O check.

[zloirock]

Thanks for the PR! Can you show a reproducible example for clarifying the problem? Some fallbacks for IE11 Script Access Denied already added.

[zloirock]

@doctyper so what about a reproducible example?

[doctyper]

@zloirock It's very difficult to abstract this into a reproducible example.

We use a React stack using Babel to transpile our code. Babel uses core-js to shim functionality, and that's where the bug surfaces for us.

I've tried to reproduce the error using just core-js but the fact that the bug only occurs on IE11/IE Edge makes this a very tedious process.

I do believe this is in some way similar to the fallbacks you added (I used them to track down this bug as well).

[zloirock]

The main problem here - ({get [Symbol.toStringTag](){ throw 42 }}) + '' should throw error by the spec, but with try / catch it will not work. And performance issue (it's also used for classification objects in some cases). I also can't reproduce it. Need to think what we can do.

[zloirock]

Still can't reproduce it, but OK, added this fallback.