Root Cause:
The color of center marker is wrong.
Next:
The color of center marker is white when dark theme is enabled; Otherwise, it's black.
Bug: 159028208
Test: manual test & make RunSettingsRoboTests ROBOTEST_FILTER=BalanceSeekBarPreferenceTest & make RunSettingsRoboTests ROBOTEST_FILTER=BalanceSeekBarTest
Change-Id: Id2d548778d1275709448f4c009a8469216950d8c
Merged-In: Id2d548778d1275709448f4c009a8469216950d8c
(cherry picked from commit 34a873884d)
This adds an audio balance slider to accessibility allowing the end
user to adjust the audio balance between left and right channels.
Test: Change Balance through Settings, play audio
Bug: 28390736
Change-Id: I70f22d222ea310fd33ebe4f3fb054f44f69d2548