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This is a follow-up CL of the original:
https://chromium-review.googlesource.com/c/chromium/src/+/2253363/

Upon shown, wake lock will only be requested when the battery is
charging, and also be release when the charger is disconnected later.

Bug: b/159382866
Test: covered by unittests.
Change-Id: I62d94d645a67c07c2310b6d1a7ee8220a24c77f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2259773
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782060}