Draw splash window during app switch if the top activity is not drawn.

In Wear OS, when the device enters ambient mode, we will switch the front activity to the background. When device exits ambient mode, the previous activity will be moved back to the front. If the activity hasn't been drawn yet when the device enters ambient mode, we want to show the splash window when it's brought back to the front.

Bug: 176837715
Bug: 199552234
Fix: 199552234
Test: manual test
Change-Id: I8275db9cb51575b61f5a4f04316b77e3f53ba220
(cherry picked from commit 3dc923bafc4454490935fd9e6b4b6602a91febaf)