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This makes use of COLOR_TAB_THROBBER_SPINNING in both the loading and
waiting states.

Bug: chromium:903457
Change-Id: I3e6bed8392c956604649c42eb8fcef1d10a7a8c9
Reviewed-on: https://chromium-review.googlesource.com/c/1329349Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607270}