Fix testOverrideSplashscreenTheme flaky by preventing from double launch The test flaky because there could start activity twice before first activity destroyed, so there didn't set the theme correctly. Add an extra callback to preventing from double start activity. Fixes: 194120010 Test: run "atest SplashscreenTests" several times Change-Id: I510f1e9190c69f2a4f3d0a35ccb7fa96dbee1e32