GitLab

This histogram will track how often the migration before handshake ends
up with success, and how often is not.

Bug: 790547
Change-Id: I8cb9c3dbcbb7262955c69284f1a12d2e11be61eb
Reviewed-on: https://chromium-review.googlesource.com/c/1315933
Commit-Queue: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605453}