Recover from Throwable in FileRotator, dump.

In rewriteSingle(), catch Throwable to rollback to backup file,
instead of just IOException. Also add dumpAll() to pack up contents
for later debugging, and use it when encountering bad stats.

Bug: 6467868
Change-Id: Ic8e287cf5a235706811a304a88d71d11d3a79cd4
4 files changed