Bug(focus-trap): MS Edge: Shift-Tab goes out of the trap

[holo-michael-simarta]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

Shift tab should go to the last element of the dialog

What is the current behavior?

Shift tab goes to

and does not reforcus, then continuing to shift tab would go the elements in the background of the dialog.

What are the steps to reproduce?

https://plnkr.co/edit/fGnZezVKDAcjOapZ5IyV?p=info

What is the use-case or motivation for changing an existing behavior?

A11Y

Which versions of Angular, Material, OS, browsers are affected?

Angular 2.4.5
Material 2.0.0-beta.2

Windows 10
Microsoft Edge 38.14393.0.0
Microsoft EdgeHTML 14.14393

Is there anything else we should know?

It is expecting a md-dialog-actions to find where the last item is but we want the actions to be beside the title. Current workaround right now is to specify the absolute position of the md-dialog-actions which is not ideal.

[devversion]

This issue only seems to appear inside of <iframe> element, and Edge just prints Script5 Error: Access Denied.

I tracked it down to the isTabbable method that tries to access the frameElement, which is obviously critical to MS Edge.

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