Fake the cache size to be 0 bytes when cleared.

The fast track storage calculation returns a non-zero answer after
the storage has been cleared. The simplest workaround here is to
fake the size as 0 bytes in the view after cache clearing.

It will not be zero if the user exits and comes back, but this
should be fine.

MARK IT ZERO!

Change-Id: Ia012c2cf2842040d5eac3d4a72539ec7dcfb9570
Fixes: 34965659
Test: Settings Robotest
(cherry picked from commit bf1f8e9c)