Act on scrim visibility

The scrim visibility drives whether the launcher window is opaque or
not. We should track it and apply the flag instead of trying to catch it
through other Launcher life cycles.

Fixes: 195365607
Bug: 196403152
Test: tap on home button while launching app from overview
Change-Id: I2a00b86b602b5dd12c901433b92adcf0170be15e
(cherry picked from commit e4a94691)