This is a follow-up to  issue 245392 , for which we implemented a metric to measure how many bookmarks users have, in total.

We might want to have some additional, more fine-grained metrics around bookmarks usage, such as:
  * How many bookmarks are on the Bookmarks Bar vs. under Other Bookmarks?
  * How many bookmarks are top-level on the Bookmarks Bar, vs. in subfolders?
  * How many folders are top-level on the Bookmarks Bar?
  * How nested are bookmarks in general?
  * How many bookmarks do users actually use/click on/navigate to after bookmarking? Ideally, we'd be able to understand this relative to the number of bookmarks they have.
  * How nested are the bookmarks that actually get used?

Which specific metrics we implement really depends on what we ultimately hope to achieve by understanding this data.