Enable per thread heap for database thread

BUG=591606

Committed: https://crrev.com/993e3a74102e0843bebb2f52de1a904f151843d4
Review-Url: https://codereview.chromium.org/1909813002
Cr-Original-Commit-Position: refs/heads/master@{#397383}
Cr-Commit-Position: refs/heads/master@{#398558}
19 files changed