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These were some of the augmentations that came out of a review
session with the UX designer:

- Make sure the Play button disappears while seeking.
- Enlarge the Play/Pause button.
- Fill in the holes of the Play/Pause buttons and change
  the transparency colors.
- Shrink the background gradient and make it non-linear (make
  it tail off quickly towards the end).
- Set Pause image asset as the default icon (to avoid flashing
  from Play to Pause when playback starts).
- Adjust the margins a bit, especially to increase bottom padding
  to lift controls at bottom up a bit and set the proper space
  between them.
- Increase the font for Time Remaining.
- Make the SeekBar track a little thicker.

TBR: bsazonov@chromium.org
Screenshots: https://crbug.com/895776#c47
Bug: 895776, 656015
Change-Id: Id288dc836df4d7b835fd1e148f1d5e0335aca764
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2183936Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771354}