VideoPlayer: Fix accessibility issues.

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.

Committed: https://crrev.com/e658ee09f499f70c2bbb5589acaf4b35f6bd13d9
Cr-Commit-Position: refs/heads/master@{#359300}

[fukino, 2015-11-12 09:25:46]

Description was changed from

==========
VideoPlayer: Fix accessibility issues.

BUG=551267,533604
TEST=manually
==========

to

==========
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.
==========

[fukino, 2015-11-12 09:33:19]

fukino@chromium.org changed reviewers:
+ mtomasz@chromium.org, yawano@chromium.org

[fukino, 2015-11-12 09:33:19]

mtomasz@: PTAL at
chrome/browser/chromeos/extensions/file_manager/private_api_strings.cc.
yawano@: PTAL at others.

Thank you!

[mtomasz, 2015-11-12 09:55:10]

lgtm for strings

[yawano, 2015-11-12 10:15:44]

lgtm. Thank you!

[fukino, 2015-11-12 10:38:16]

Thank you!

[fukino, 2015-11-12 10:38:22]

The CQ bit was checked by fukino@chromium.org

[commit-bot: I haz the power, 2015-11-12 10:38:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1435253002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1435253002/1

[commit-bot: I haz the power, 2015-11-12 10:42:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-12 20:06:34]

Patchset 1 (id:??) landed as
https://crrev.com/e658ee09f499f70c2bbb5589acaf4b35f6bd13d9
Cr-Commit-Position: refs/heads/master@{#359300}