The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dba97641da1b5469466c993a94993e3e6ed85963

commit dba97641da1b5469466c993a94993e3e6ed85963
Author: Siddhartha <ssid@chromium.org>
Date: Mon Feb 12 21:19:57 2018

Reduce the write buffer size of history report databases

The write buffer sets threshold at which items are written to disk.
The history report databases are updated with new key once per page load
and cleared periodically with calls from system. The in-memory write
buffer is not really useful for performance in this case. So, the write
buffer size is reduced from 4MB to 500KB. This only increases rate at
which items are evicted, not the amount written to disk.
Having a large write cache also affects startup performance by loading
more items in the db.

BUG= 809762 

Change-Id: Ib82c3f363e7f3af373403dad139aac593cf12144
Reviewed-on: https://chromium-review.googlesource.com/905238
Commit-Queue: Siddhartha S <ssid@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536192}
[modify] https://crrev.com/dba97641da1b5469466c993a94993e3e6ed85963/chrome/browser/android/history_report/delta_file_backend_leveldb.cc
[modify] https://crrev.com/dba97641da1b5469466c993a94993e3e6ed85963/chrome/browser/android/history_report/usage_reports_buffer_backend.cc