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Adds a Histogram interface with two implementations. One for
ratios with most of it's precision just above 1 and another
for latency with higher precision near vsync intervals.

The Histogram can be queried for approximate percentiles,
which will be useful for UKM based frame metrics.

Bug: 807463
Change-Id: I83b251e2d50166cd4c376a10050ee344e312368f
Reviewed-on: https://chromium-review.googlesource.com/972194Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Brian Anderson <brianderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544754}