Log histogram of fsync times of sharedPreferences

Example log:

Time required to fsync
/data/user/0/com.google.android.gms/shared_prefs/gms_sync_prefs_sync:ContactMetadata.xml:
[<1: 0, <2: 0, <4: 0, <8: 0, <16: 0, <32: 0, <64: 0, <128: 0, <256: 0,
<512: 0, <1024: 1, <2048: 0, <4096: 0, <8192: 0, <16384: 0, >=16384: 0]

Fixes: 30662828
Test: Looked at log
Change-Id: I6d585b107ae14e05ff1c77b0a0017de684226cba