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Add more UMA to track the performance and correctness
of the resource loading hints experiment. Specifically,
this CL records UMA on how many page hints are
received via component updater, and how frequently
were the resource hints available at the time
of page commit.

Bug: 878129
Change-Id: I8bc3dd1e6d7c80e4cefc34ebb6119665d5fbee5e
Reviewed-on: https://chromium-review.googlesource.com/1197108
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587944}