Fix Bubbles flying away and never returning.

See http://b/153525851#comment5 for context.

Test: have bubbles and pip, repeatedly dismiss and add PIP and notice you can happily bubble as usual instead of them flying away or hiding under the nav bar
Fixes: 153525851
Change-Id: I0b107c4cad6caada1a93a9c1fe69302d637e305b