Don't touch usage stats before system ready

When a content provider is accessed we update its foreground
state and usage stats if the calling app is in the foreground.
However we install system providers before the
PHASE_SYSTEM_SERVICES_READY phase which means we cannot touch
the the usage stats service as it calls into the content
service triggering the sync manager creation before system
ready violating the contract of the latter causing cascading
issues.

bug:31562236

Change-Id: Ied446cf3de8949e0850bab8f2b92155eac793591