[Contextual Search] Add metrics to track Taps before Open.
Adds several new histograms for Contextual Search to track:
The total number of taps before ever opening the promo panel,
the number of times the promo panel was opened, the number
of taps since any panel was opened, and information about the
search term resolution (protocol, and single/multi-word).
There's a downstream CL dependent on this change: https://chrome-internal-review.googlesource.com/#/c/216388/
BUG=477827
Review URL: https://codereview.chromium.org/
1131653005
Cr-Commit-Position: refs/heads/master@{#330841}