Video Player WebUI: replace paper-slider with cr-slider

The video player progress needs to be updated from the slider value
only when the change is due to a user interaction. For this
reason cr-slider-value-changed-from-ui was introduced.

cr-slider getRatio() was made public since it is meaningful
representation of the slider value.

Swapped the skip direction of ArrowLeft/ArrowRight when the text
direction is RTL.

When the volume value is changed with the keyboard and the media
controls are hidden, the media controls are shown.

Bug: 902873
Change-Id: Ide0a23783274d4c11ea83b367aba8b41a5dd8ad1
Reviewed-on: https://chromium-review.googlesource.com/c/1357216
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613384}
7 files changed