Update window always on convertTo/FromTranslucent

Previously we would only update the window if the activity's
translucency was changed. That meant that if the window was
opaque for a translucent activity, transitioning to translucent
would not change the window to translucent. This change forces
the window to follow the convertToTranslucent and
convertFromTranslucent calls.

Also fix for setting background on enter and exit transitions.

Partial fix for 16215650.

Change-Id: I86ea68e4bbf604d0cc60cc6e34bf8090199525d6