cannot add aria label to mat-tab

[literalpie]

Bug, feature request, or proposal:

This seems to be a bug

What is the expected behavior?

Adding the aria-labelattribute to the mat-tab element should allow screen-readers to read the label of the element, even if the element has no text.

What is the current behavior?

If there is a mat-tab that has an Icon label, but no text, and you try to put an aria-label on the mat-tab the aria-label is removed from the element.

What are the steps to reproduce?

https://stackblitz.com/edit/aria-in-mat-tabs?file=app/tab-group-custom-label-example.html

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

a11y

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

Angular 6.0.x and material 6.3

Is there anything else we should know?

[angular-automatic-lock-bot]

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