Add @GuardedBy annotation to PersistentDataBlockService#mIsWritable.

Change-Id: I1024f2a56badde5c123d025d6fe02f42559cbcb1
Test: manual
Bug: 30352311
(cherry picked from commit f6f1d627483b4dad9d65176769a1ee92c59a4810)
(cherry picked from commit 71d2a41dd9c8be8c4bca5eba339802e1e0c2be3c)
1 file changed