debugGlassWalkFallback top-level property
Whether the host's capture hands a subtree the walk draws apart from the
engine to the engine (ProxyWalkContext.fallbackPixelRatio): an opacity
folded into a filter below it, a shader mask that paints past its
children. On; a benchmark turns it off to price it, and sets it back.
Implementation
bool debugGlassWalkFallback = true;