GitLab

-Add WebViewAppStateObserver.
-Notify app state change through AwContentsLifecycleNotifier.

Bug: 1042048
Change-Id: Ide14e8583e78b4597fcd061c9dabacf2cb35fe61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015407Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Tao Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735197}