The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/50fa83290a2937f8b7f90b109130786d039fa5b9

commit 50fa83290a2937f8b7f90b109130786d039fa5b9
Author: Josh Karlin <jkarlin@chromium.org>
Date: Mon Mar 05 22:39:42 2018

[PageLoadMetrics] Measure time on page before pressing back button

For navigations which are initiated by user gesture, measure how long the user
stays on the page if they press the back button.

Bug: 817846
Change-Id: I1b2831b133f1856be8bf18c36d5df3d88e1610de
Reviewed-on: https://chromium-review.googlesource.com/943702
Commit-Queue: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540964}
[modify] https://crrev.com/50fa83290a2937f8b7f90b109130786d039fa5b9/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
[modify] https://crrev.com/50fa83290a2937f8b7f90b109130786d039fa5b9/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
[modify] https://crrev.com/50fa83290a2937f8b7f90b109130786d039fa5b9/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer_unittest.cc
[modify] https://crrev.com/50fa83290a2937f8b7f90b109130786d039fa5b9/chrome/browser/page_load_metrics/page_load_metrics_observer.h
[modify] https://crrev.com/50fa83290a2937f8b7f90b109130786d039fa5b9/tools/metrics/histograms/histograms.xml