It would be really nice for impact and knowledge reasons to add UserAction metrics to the Applications panel in DevTools.

The following categories could signal a USerAction when the user clicks on them:
* Manifest
* Service Workers
* Clear Storage
* Children of Local Storage
* Children of Session Storage
* Children of IndexedDB
* Children of children of IndexedDB
* Children of Web SQL
* Children of Cookies
* Children of Cache Storage
* Children of Application Cache

Main reason for this is to demonstrate how much impact / how many eyeballs are on changes that Kristi makes.

This should be a simple change - either there are hookups in JS for devtools for user actions, or you can make a quick binding somewhere that calls:
https://cs.chromium.org/chromium/src/base/metrics/user_metrics.h?q=base/metrics/user_metrics.h&dr&l=47

And then I believe update an xml file in tools/metrics