[accessibility] Autocomplete should use role=combobox

[tirana]

from https://www.w3.org/TR/wai-aria/roles#combobox
"Typically editable combo boxes are used for autocomplete behavior, and authors SHOULD set aria-autocomplete attribute on the textfield."

[ThomasBurleson]

@marcysutton - can you review ?

[marcysutton]

Is a fix for an issue with the usability of the autocomplete, or have you tested it? I know of one issue that is open related to this, but it worked correctly in a variety of browser and AT combos when we chose the current semantics. #6042

[tirana]

1. a user who is blind reported an issue with a search box. the our search box is md-autocomplete.
   the element has annotation for screen reader yet it's incorrect.
   our accessibility QA said that role was wrong.
2. I looked at google.com search box which had similar logic and found that role=combobox was used.
3. I looked at the doc and found that combobox is recommend role for autocomplete input fields. https://www.w3.org/TR/wai-aria/roles#combobox

testing: I uses http://www.chromevox.com/ for testing.
using dev tool I manually changed role and compared description
edit text vs combobox autocompletion

[tirana]

BTW, #6042 the first point is exactly the same what I did
Remove role="listbox" from <md-autocomplete-wrap>, add role="combobox" to <input>,

[tirana]

@marcysutton Does it make sense?

[marcysutton]

Makes sense to me, I just don't have time to test it at the moment. If you can confirm it still works with the Material-supported browsers and a few screen readers, that would help a lot. Some good targets for that would be Firefox/NVDA, Safari/Voiceover, and optionally IE11 and JAWS (which has a free 40 minute mode). Chromevox nor Chrome/Voiceover are widely used, so we didn't focus on those in the past.

[tirana]

confirmed. combobox sounds better

[marcysutton]

Yay, that's great! LGTM, ship it!