Add two histograms to collect data on number of queued packets

when packets go out of order.

Bug: 817496
Change-Id: Id0d0a987bd46664ab68ba04fe7134b4d19fee8e8
Reviewed-on: https://chromium-review.googlesource.com/941388


Commit-Queue: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540275}