[bfcache] Track presence of IndexedDB connection for bfcache metrics

In addition to tracking of outstanding IndexedDB transactions, also
track database transactions.

R=haraken@chromium.org,dmurph@chromium.org
BUG=966056

Change-Id: I4c426e3866c74a36b3dc2be1a62c52cb5a7f77b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625120
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662457}
4 files changed