GitLab

This commit simplifies the logic of AccelerometerProviderMojo by
limiting the usages on the UI thread.

BUG=b:175355860
TEST=unit tests and run on kohaku(hatch)

Change-Id: Ic43439a70b544848dcd3a948f996f81a9032687d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586172Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Cheng-Hao Yang <chenghaoyang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839061}