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The refactor of the hints manager unittest and metrics recording is
not strictly required but done in the below CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1762982

This is mostly to reduce the amount of merge conflicts I will get

Bug: 969558
Change-Id: I49d7afc1a977bc2111dedc48fdd5cf5e3c022184
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1772476
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690925}