1. Added Eject Icon for Roots that support eject
2. Added Context Menu for RootsFragment (Settings and Eject)
Bug: 29584653
Change-Id: I97f582de05763e3f0327bc0d2dc6d4e2222e047c
(cherry picked from commit d96661f8b0f613b40f2bdfc178bbe06022b5f76c)
Also, reveal the illusion that we're restoring state in Files and Downloads.
Also, define a "PairedTask" class that guards calls to task methods
with checks against isDestroyed. This also let us make all of the tasks
static, so we get much narrower scope and tasks can even be moved to
their own files.
Change-Id: I6a9e8706e1ab1d1f43301e73dd9858a115a6baaf