There should be a way to check CKEditorError with parameters

[Reinmar]

Moved from https://github.com/ckeditor/ckeditor5-core/issues/68

[Reinmar]

Turns out this will be needed because of compatibility with ES5: https://github.com/ckeditor/ckeditor5-dev-compiler/issues/18#issuecomment-240718336.

[Reinmar]

We've been originally thinking about extending Chai by adding expect().to.throwCKEditorError(). I'm a bit afraid of doing this, but otherwise, we'll not be able to use this function at all.

I was also thinking about adding isCKEditorError( err, [ msgPattern ] ) function (and exporting it) to the utils/ckeditorerror module. This function will then be usable in the dev code. The Chai's extension would of course use this function.

[maxbarnas]

I've added static method isCKEditorMethod to utils/ckeditorerror. This implementation is still not valid in code transpiled to ES5.

[Reinmar]

I've added static method isCKEditorMethod to utils/ckeditorerror. This implementation is still not valid in code transpiled to ES5.

Could you put it on review?

[maxbarnas]

I set this as invalid because of problems with Chai extension in bundles. We'll use Babel plugin, that allows to extend builtin types - this will make instanceof usable again.