Also consider some time-of-day bucket histograms when some conditions are met. 
For example, perhaps histogram of local hour of the day for:
  1. Wifi connection and over 50% battery [potential speculative load conditions]
  2. Mobile connection and over 50% battery [potential user requested load conditions]

We decided to delay adding the UMA until we have decided to implement speculative background loading.  This is delayed until we get privacy concerns addressed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2

commit 1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2
Author: petewil <petewil@chromium.org>
Date: Fri Jun 03 16:49:29 2016

Add UMA to measure request latency time.

Now that we are actually using the scheduler and GCM Network Manager,
add the UMA to measure how long the user's request took from request
until the network came back.

BUG= 597364 

Review-Url: https://codereview.chromium.org/2032833002
Cr-Commit-Position: refs/heads/master@{#397730}

[modify] https://crrev.com/1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/BackgroundOfflinerTask.java
[modify] https://crrev.com/1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/BackgroundScheduler.java
[modify] https://crrev.com/1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageUtils.java
[modify] https://crrev.com/1ea1c6e4c0b98c497cb518a4454ddf3bb6fb76b2/tools/metrics/histograms/histograms.xml