GitLab

1. Add Delete all function for both content and jornal.
2. Update DeleteContentByPrefix to use
   leveldb_proto::UpdateEntriesWithRemoveFilter.
3. Fix FakeDB<T>::UpdateEntriesWithRemoveFilter the way to handle
   erase during iteration.

Bug:831633

Change-Id: I7ae4df74244b3c3ac5c0bf36ea2e2bdc7839d375
Reviewed-on: https://chromium-review.googlesource.com/1103939Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Filip Gorski <fgorski@chromium.org>
Commit-Queue: Gang Wu <gangwu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568224}