md-tab-nav-bar: ink doesn't change with resizing tabs

[willshowell]

Bug, feature request, or proposal:

Bug

What is the current behavior?

When the window hits the $mat-xsmall breakpoint, min widths for .mat-tab-label and .mat-tab-link change from 160px to 72px. The ink bar does not reflect that.

What are the steps to reproduce?

http://plnkr.co/edit/6NlXoXhzaDHsHtTo9JWn?p=preview

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

Master

Other Info

Related to #3044 but does not require tabs to be stretched.

[jelbourn]

Dupe of #3044

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