Propagate light nav bar info

When SystemUI (notification UI) is pulled down, the windows behind are
dimmed, including navigation bar. At this point of time, navigationbar
color could be controlled by IME and system overrides it.
With this fix, we check if IME is already controlling navbar color.

Change-Id: I9f25860a5b7858f1d17d2921816910a938c656bb
Fix: 122439339
Test: Manually verified using steps in bug.