Replace reflection with Suppliers.

Reflection was causing proguard to turn the empty constructors on
Behavior classes into NPE's. I don't know why it does this, but
removing reflection from the code seems to resolve the issue.

Fixes: 221190784
Test: manual && atest SystemUITests
Change-Id: I5f45e9c06b6c466d666057a056537a08afd9c9ec