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This CL adds the methods to track the user's first interactions with the
Translate UI, and the total number of interactions over the course of a
page load. These values will later be logged to UKM. The CL includes the
Translate compact infobar UI, but the bubble UI will be added in a later
CL.

Full design doc: https://docs.google.com/document/d/1dyWh1Xw5VgUA00VA-5PTgKQ6ItziPBnSyeDR8saJ9vM/edit?usp=sharing

Bug: 1114868
Change-Id: I03b3945c2af1c05431907b1eb15fef5e4b1a5fbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572129
Commit-Queue: Max Curran <curranmax@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840830}