[flexiglass] Blind fix for ShadeStartableTest

The test doesn't fail locally but seems to file in automation. The
assert on line 180 is failing but there's a suppressed exception right
below it where the "root: View" property of the depth controller isn't
initialized before it's accessed.

Bug: 411567853
Test: Wasn't able to test it
Flag: EXEMPT - test fix only
Change-Id: Ic6557e1de479887941ef2f0f703cfaf30ced2c77