First step:
Create a webpage that uses indexeddb, and you can trigger a database upgrade that changes the object stores (change # of object stores, or just the name - each change will be a version upgrade).

Then you can do your devtools changes.

Alternatively, you can look at the devtools testing infrastructure (see example cls of mine from a couple years ago) and do test-first development:
https://codereview.chromium.org/1131723005/
https://codereview.chromium.org/1111563006/

Either way, you'll need to end up with testing :P

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/075f218d5fc98ed1738637f05354ce9a3b0cb831

commit 075f218d5fc98ed1738637f05354ce9a3b0cb831
Author: kristipark <kristipark@chromium.org>
Date: Wed May 31 02:03:02 2017

Added a refresh database button on the IndexedDB view.

BUG= 723871 

Review-Url: https://codereview.chromium.org/2902673003
Cr-Commit-Position: refs/heads/master@{#475739}

[add] https://crrev.com/075f218d5fc98ed1738637f05354ce9a3b0cb831/third_party/WebKit/LayoutTests/http/tests/inspector/indexeddb/database-refresh-view-expected.txt
[add] https://crrev.com/075f218d5fc98ed1738637f05354ce9a3b0cb831/third_party/WebKit/LayoutTests/http/tests/inspector/indexeddb/database-refresh-view.html
[modify] https://crrev.com/075f218d5fc98ed1738637f05354ce9a3b0cb831/third_party/WebKit/LayoutTests/http/tests/inspector/indexeddb/indexeddb-test.js
[modify] https://crrev.com/075f218d5fc98ed1738637f05354ce9a3b0cb831/third_party/WebKit/Source/devtools/front_end/resources/IndexedDBViews.js