Audio Player: replace paper-slider with cr-slider

The audio player's progress slider uses sliders in a different way from
other sliders in settings. The value of the slider is updated
frequently when playing. While the knob is being dragged, audio
playback is paused and is resumed when the drag completes.

Previously the audio player was using the immediate-value-changed and
value-changed events to determine if the knob was being dragged.

A couple changes were required to support the audio player progress
slider. When the |dragging| property is changed, the |dragging-changed|
event is dispatched. And the slider |value| is updated after dragging
has started and before dragging has completed. This allows the audio
player to pause playback, ignore any subsequent updates to the progress
and accept changes to progress during dragging. When dragging is done,
the audio player has access to the most up-to-date value of the slider
so it can update the time of playback then resume playing.

Inverting the direction of ArrowRight/ArrowLeft keybindings when the
direction is RTL.

Bug: 902873
Change-Id: I898889fc882ef0b1459ceabf8d27ed5ad62267c0
Reviewed-on: https://chromium-review.googlesource.com/c/1325012
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@{#610339}
9 files changed