[Contextual Search] Add currently-private histograms.
[Contextual Search] Add currently-private histograms.

We have a large set of histograms that were set up private
before our feature launched, that should now be public.
This adds those existing histograms.
Removing the private ones will be done soon in the private
repository.

BUG=545055

Review URL: https://codereview.chromium.org/1441013004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#361229}

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