This is the tracking bug for landing UKMs to track usage of sharing-related functionality, split by website. This will, for example, tell us what kinds of verticals users are frequently sharing.

The specific metrics we're interested in splitting by URL are:
- (Android) User clicked the share button (either from the three-dot overflow menu or from the bottom toolbar, for certain versions of the Duet experiment). Currently captured with MobileMenuShare and MobileMenuDirectShare user actions.
- (iOS) User clicked the share button (from the omnibox). Currently captured with MobileToolbarShareMenu user action.
- (Android) User took a screenshot. Currently captured with Tab.Screenshot user action.

If I think of any more, I'll add them.