a degree of randomness (including drop outs) would be useful to reproduce real world connectivity  

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8a4e4200086bc67a61c83d60edfb450844377e5a

commit 8a4e4200086bc67a61c83d60edfb450844377e5a
Author: chenwilliam <chenwilliam@chromium.org>
Date: Mon May 15 23:56:14 2017

DevTools: simplify network throttling presets

BUG= 721112 

Review-Url: https://codereview.chromium.org/2876683002
Cr-Commit-Position: refs/heads/master@{#471950}

[modify] https://crrev.com/8a4e4200086bc67a61c83d60edfb450844377e5a/third_party/WebKit/Source/devtools/front_end/Tests.js
[modify] https://crrev.com/8a4e4200086bc67a61c83d60edfb450844377e5a/third_party/WebKit/Source/devtools/front_end/network_conditions/NetworkConditionsSelector.js
[modify] https://crrev.com/8a4e4200086bc67a61c83d60edfb450844377e5a/third_party/WebKit/Source/devtools/front_end/network_conditions/NetworkConditionsSettingsTab.js

@zac.spitzer - thanks for the feedback. We considered introducing variance, which is significant for 3G in developing areas, but for now we have decided to not include variance as other tools such as Lighthouse (https://github.com/googlechrome/lighthouse) benefit from a low-variance throttling tool as some of their use case is for CI bots.

If you do want to simulate packet loss and happen to use Mac, I would look into Network Link Conditioner which simulates packet loss and is easy to use. If you're on Windows, there's a tool called WinShaper that I haven't personally used but it looks promising https://calendar.perfplanet.com/2016/testing-with-realistic-networking-conditions/.