VideoPlayer: Fix accessibility issues.
This CL is video-player part of https://codereview.chromium.org/1415953006/.
As we decided to punt audio player's redesign, this CL includes changes only for video player.
This includes:
- Make each control focusable.
- Implement blue outline for focused-by-keyboard buttons.
- Add aria-label for buttons and sliders.
- Extracted common behaviors of icon buttons as files-icon-button.
BUG=551267,533604
TEST=manually tested using ChromeVox.
Review URL: https://codereview.chromium.org/1435253002
Cr-Commit-Position: refs/heads/master@{#359300}
10 files changed
