The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c0ea3a88790aae1811a30b2aa21aca02646a71f

commit 2c0ea3a88790aae1811a30b2aa21aca02646a71f
Author: Andreas Butler <andreasbutler@google.com>
Date: Thu Nov 29 23:47:07 2018

[IndexedDB]: Add use counter to IDB databases.

Adds a UMA use counter to IDBFactory.databases().

Bug:  909000 
Change-Id: I3a45c7cccec208fa8d9227bcfb2cc24a4a688324
Reviewed-on: https://chromium-review.googlesource.com/c/1352484
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Andreas Butler <andreasbutler@google.com>
Cr-Commit-Position: refs/heads/master@{#612442}
[modify] https://crrev.com/2c0ea3a88790aae1811a30b2aa21aca02646a71f/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/2c0ea3a88790aae1811a30b2aa21aca02646a71f/third_party/blink/renderer/modules/indexeddb/idb_factory.idl
[modify] https://crrev.com/2c0ea3a88790aae1811a30b2aa21aca02646a71f/tools/metrics/histograms/enums.xml