a11y: macOS VoiceOver reads out a wrong command to use the slider

[takumif]

Description

VoiceOver tells users to control a slider using ctrl-option-left/right, but it's actually controlled with shift-left/right.

Expected outcome

Either:

• The sliders are controllable with ctrl-option-left/right OR
• VoiceOver should say the sliders are controllable with shift-left/right

Actual outcome

Neither of the above

Live Demo

https://www.webcomponents.org/element/PolymerElements/paper-slider

Steps to reproduce

• Enable the VoiceOver screen reader on macOS and visit a page with a paper slider
• Use tab and ctrl-option-shift-up/down to get inside the slider
• Note that VoiceOver says to use ctrl-option-left/right to use the slider (may need to exit/enter the slider using up/down keys to have this read)
• Note that the slider cannot be controlled with ctrl-option-left/right. Instead, shift-left/right works.

Browsers Affected

Tested on Chrome M61/62. The bug is affecting the Cast WebUI dialog.

• [x] Chrome
• [ ] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10

[keanulee]

Can confirm that this is an issue. Not sure how to fix it though - because unlike the native<input type="range"> slider, there's no standard browser API to hook into screenreader shortcuts that I am aware of.