Proposal: Smart Group Profiler to help identify slow smart groups

Slow smart groups are a problem that I'm sure we've all experienced. It's difficult for users to guess which of their potentially many smart groups is exceptionally slow or if they just have too many, each taking a little time. @JonGold has a profiling script, but that's not accessible to many. I'm sure many orgs would be happy to cut or re-work their slow smart groups if it meant they could use the listing accordion on individual contacts, etc — but they just don't know which ones they need to cut!

What I propose is a Smart Group Profiler in Admin that lets admin users easily check their smart groups in the UI. Here's a quick sketch:

• The user can select groups to profile or leave the select empty to profile all (active, non-hidden) smart groups
• The user can select to run once or average up to three times, to reduce the potential for random variation
• The profiler queues CRM_Contact_BAO_GroupContactCache::add for each group, in random order
• Once the queue finishes, the user gets a table with average time and links to edit the Smart Group criteria for each

I'd be happy to do this as an extension, but it also seems like something that address a core problem, so I think it makes sense to have in core.