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Since there are situations where bottom pregress bar shows and mid overlay hides,
we are going to have different hide timer for them. This CL add a hide timer logic
into touchless element base class so that all sub element can have the hide timer
(This is also a preparation for volume indicator hide timer).

Bug: 942153
Change-Id: I980f1ec4439cad233a321a98bf1f2e6a535338eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1570128
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652198}