The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0c3532027893052475cd87ac0f6c758046f34415

commit 0c3532027893052475cd87ac0f6c758046f34415
Author: bmcquade <bmcquade@chromium.org>
Date: Tue Apr 18 02:34:49 2017

Add detailed tracking for causes of invalid PageLoadTimings.

In https://codereview.chromium.org/2804093002 we added additional error codes
to understand the root cause of ERR_BAD_TIMING_IPC. New data shows that
ERR_BAD_TIMING_IPC_INVALID_TIMING is the primary cause.

We know we are receiving invalid PageLoadTiming structs, but we don't yet know
the specific cause. This change adds more detailed error codes to get insight
here.

BUG= 712033 

Review-Url: https://codereview.chromium.org/2820943002
Cr-Commit-Position: refs/heads/master@{#465108}

[modify] https://crrev.com/0c3532027893052475cd87ac0f6c758046f34415/chrome/browser/page_load_metrics/metrics_web_contents_observer_unittest.cc
[modify] https://crrev.com/0c3532027893052475cd87ac0f6c758046f34415/chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc
[modify] https://crrev.com/0c3532027893052475cd87ac0f6c758046f34415/chrome/browser/page_load_metrics/page_load_tracker.cc
[modify] https://crrev.com/0c3532027893052475cd87ac0f6c758046f34415/chrome/browser/page_load_metrics/page_load_tracker.h
[modify] https://crrev.com/0c3532027893052475cd87ac0f6c758046f34415/tools/metrics/histograms/histograms.xml