This shouldn't change the opt out rate if we're using the "Infobar shown" bucket as the baseline and not summing all dismissal types to get that value. 

Good point. Seems like a P3 then since we only care about shown vs clicked link really.

Ya, I don't think it's necessary to merge this either. Moving to M60.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e111e380e8f4178c4a1907c4fa6b4408a22800bc

commit e111e380e8f4178c4a1907c4fa6b4408a22800bc
Author: megjablon <megjablon@chromium.org>
Date: Mon Apr 17 21:53:47 2017

Track Previews infobar dismissals due to tab closure

BUG= 706528 

Review-Url: https://codereview.chromium.org/2820793003
Cr-Commit-Position: refs/heads/master@{#465032}

[modify] https://crrev.com/e111e380e8f4178c4a1907c4fa6b4408a22800bc/chrome/browser/previews/previews_infobar_delegate.cc
[modify] https://crrev.com/e111e380e8f4178c4a1907c4fa6b4408a22800bc/chrome/browser/previews/previews_infobar_delegate.h
[modify] https://crrev.com/e111e380e8f4178c4a1907c4fa6b4408a22800bc/chrome/browser/previews/previews_infobar_delegate_unittest.cc
[modify] https://crrev.com/e111e380e8f4178c4a1907c4fa6b4408a22800bc/tools/metrics/histograms/histograms.xml