Instant Search: Make it possible to configure `w.js` ( Tracks ) to only use a short-lived in-memory anon ID

[bperson]

Following the merge of #13730, I tested it further and the default behavior of w.js is to rely on cookies, we should explore how we can have the kind of short-lived non-tracking-across-pageviews anonID mentioned in this comment.

Steps to reproduce the issue

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

What I expected

What happened instead

Screenshots
If applicable, add screenshots to help explain your problem.

[jsnmoon]

It seems like this is happening because send invokes loadIdentity. What do you think about performing clearIdentity on page load? This would ensure that the user identifying cookie is reset before we send any pixels.

[gibrown]

Would that also clear the data in the browser? Or just for this page load? I don't think we want to clear the identity for logged in users, just make sure that we don't use it.

[jsnmoon]

AFAIK: it'll clear the user identification cookie and generate/assign a new anonymous cookie, thereby discarding data received from any previous invocation of identifyUser or loadIdentity.

[jsnmoon]

@bperson: This commit adds a clearIdentity call on every initial page load. Let me know what you think -- I plan on pushing this out along with #13761.

[gibrown]

I suspect that we should not clear the cookie since that may mess with other analytics we are doing elsewhere, but I don't really know enough here.

[jsnmoon]

@bperson: This commit adds a clearIdentity call on every initial page load. Let me know what you think -- I plan on pushing this out along with #13761.

The above commit has been pushed to master.