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Add the following metrics for WebSocket SafeBrowsing lookups:

* SafeBrowsing.WebSocket.Result is recorded for every WebSocket handshake that
  is checked.
* - SafeBrowsing.WebSocket.Elapsed.Safe
  - SafeBrowsing.WebSocket.Elapsed.Blocked
  - SafeBrowsing.WebSocket.Elapsed.Abandoned
  Record the time in milliseconds spent performing the SafeBrowsing lookup,
  including time spent on the interstitial page if applicable, broken down by
  result.

Because clicking "Back to safety" on the interstitial results in navigating away
from the page, it is recorded as "Abandoned", not "Blocked" as might be
expected. I haven't found a circumstance in which "Blocked" is recorded.

Tested manually with about:histograms.

Bug: 644744
Change-Id: I4ec902e122f48482c6c4d54537ce8035bbac92fc
Reviewed-on: https://chromium-review.googlesource.com/569942Reviewed-by: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488107}