track clicks to print frozen art on bulk certificate print page

[davidsbailey]

Per request in the Congrats page spec, I'm adding a metric to see how often users click the button to print frozen art. Here it is in the network tab after I click the print button:

For other clues as to how this is working:

• included on every pegasus page:

  code-dot-org/pegasus/sites.v3/code.org/views/theme_common_head_after.haml

  Line 9 in caa7b53

  %script=view 'google_analytics.js', user_type: user_type

• code-dot-org/pegasus/sites.v3/code.org/views/google_analytics.js.erb

  Lines 10 to 12 in edb52b4

  	function trackEvent(category, action, label, value) {
  	ga('send', 'event', category, action, label, value);
  	}

• code-dot-org/pegasus/sites.v3/code.org/views/google_analytics.js.erb

  Line 24 in edb52b4

  window.trackEvent = trackEvent;

• GA docs: https://developers.google.com/analytics/devguides/collection/gtagjs/events

Testing story

I've checked everything I can think of to try and track this event properly, including reading the GA docs and getting a 200 OK response in the screenshot. once it reaches production, I'll click the print button once on code.org/certificates to make sure I can see it show up somewhere in GA.

[breville]

One suggestion is to use

trackEvent('clicks', 'frozen_print_gallery', 'print')

so that we avoid adding another top-level category when browsing with the GA UI.

Also, nit: missing ;.

[davidsbailey]

thank you for your expertise here, Brendan!

[breville]

The analysis looks good here. Out of interest, there is also a handy Chrome extension for confirming that these events are working.

[davidsbailey]

frozen print clicks are starting to show up here: https://analytics.google.com/analytics/web/#/report/content-event-events/a37745279w66217109p68074336/explorer-table.plotKeys=%5B%5D&_r.drilldown=analytics.eventCategory:clicks,analytics.eventAction:frozen_print_gallery/