AX: FKA: Buttons need a visible focus indicator

AX: FKA: Buttons need a visible focus indicator
https://bugs.webkit.org/show_bug.cgi?id=171040
<rdar://problem/30922548>

Patch by Aaron Chu <aaron_chu@apple.com> on 2017-07-29
Reviewed by Antoine Quint.

Source/WebCore:

Added a background color for the focus state of the icon buttons in modern media controls.

Test: media/modern-media-controls/button/button-focus-state.html

* Modules/modern-media-controls/controls/button.css:
(button:focus):
(button:focus > picture):
* Modules/modern-media-controls/controls/slider.css:
(.slider > input):

LayoutTests:

* media/modern-media-controls/button/button-focus-state-expected.txt: Added.
* media/modern-media-controls/button/button-focus-state.html: Added.
* platform/ios-simulator/TestExpectations:
* platform/mac-elcapitan/TestExpectations:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220041 268f45cc-cd09-0410-ab3c-d52691b4dbfc