The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a8538ed261655942042ee203e2a5900a2090100c

commit a8538ed261655942042ee203e2a5900a2090100c
Author: Pete Williamson <petewil@chromium.org>
Date: Thu Dec 13 02:05:42 2018

Add UMA for catalog loading:

1. Add UMA for which path caused the load, background, EoS, or NTP.
2. Add UMA for the outcome of the load, new catalog, unchanged, or failure.

Also add unit tests for the C++ side histograms.

Bug: 910429
Change-Id: I56e06b1dcc5b7f977fd3646e199767c1194c4c02
Reviewed-on: https://chromium-review.googlesource.com/c/1357211
Commit-Queue: Peter Williamson <petewil@chromium.org>
Reviewed-by: Cathy Li <chili@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616164}
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/java/src/org/chromium/chrome/browser/explore_sites/ExploreSitesBackgroundTask.java
[add] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/java/src/org/chromium/chrome/browser/explore_sites/ExploreSitesEnums.java
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/java/src/org/chromium/chrome/browser/explore_sites/ExploreSitesPage.java
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/java/src/org/chromium/chrome/browser/explore_sites/ExploreSitesSection.java
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/java_sources.gni
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/android/junit/src/org/chromium/chrome/browser/explore_sites/ExploreSitesBackgroundTaskUnitTest.java
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/browser/android/explore_sites/explore_sites_service_impl.cc
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/browser/android/explore_sites/explore_sites_service_impl_unittest.cc
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/chrome/browser/android/explore_sites/explore_sites_types.h
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/a8538ed261655942042ee203e2a5900a2090100c/tools/metrics/histograms/histograms.xml

I have verified the fix in the latest canary.

The bug is marked as P3 or Feature. It should not be merged as M72 is in beta. 
Please contact the approriate milestone owner if you have questions.
Owners: govind@(Android), kariahda@(iOS), djmm@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot