[LargeIconService] Never expire histograms for favicon sizes

This CL sets two histograms of LargeIconService to never expire as these
histograms proved to be really useful when planning UX changes in the
past.

The favicons landscape in the wild changes constantly and thus it is
better to keep recording this to have up-to-date measurements.

Bug: 975727
Change-Id: Iedf282fbfb4d16435776111f3e37f5e6d77eb3eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663130
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Auto-Submit: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670101}
1 file changed