Navigation buttons have unhelpful aria labels on mobile

[lesliana]

Description

Chevron navigation buttons on paper tabs have unhelpful aria labels on mobile.

Steps to reproduce

1. Create a paper tab with scrollable=true and enough tabs that you see the overflow paper-icon-button.
2. On your phone, turn on VoiceOver or TalkBack.
3. Swipe through the page until you get to the paper tabs. You first get to the chevron-left paper-icon-button. Even though it's visually hidden (because you're already on the left-most tab and therefore don't need a left arrow), you hear "button" read out loud.
4. Swipe through the tabs. You hear all tab titles read. After the last tab has been read, the chevron-right button gets focus and reads "button" out loud.

It is confusing to hear "button" read before and after the tabs with no extra context. Since the right arrow is only read after all the tab names are read, it doesn't really make sense to give it a more descriptive title like "show more items", since at that point you're already at the end of the list. So maybe aria-hiding them entirely would be a better solution.

Reproduces on an iPhone with iOS10 and a Nexus 5 on Lollipop 5.1.

[Sunlis]

This is also an issue on desktop (tested with Chrome and ChromeVox). I agree that the scroll buttons should be aria-hidden.