For the new header (currently in alpha), we need to see if it has a negative impact on searches. It will not be enough to capture search button clicks (because now that is just a "header" click.
Now we also have to send an event when text is first entered into search box.
from: https://meta.wikimedia.org/wiki/Schema:Search
"session-start"
"impression-results"
"click-result"
Use cookies rather than sendBeacon to save the click-result event.