Issue 844924  has been merged into this issue.

This seems to have been done in https://chromium-review.googlesource.com/c/chromium/src/+/973811,
though for some reason the legacy path remains.

Taking this one

Not 100% sure if it's the right approach, but I uploaded a patch proposal to https://chromium-review.googlesource.com/c/chromium/src/+/1238464

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/670a583f75224581a26338b3c4f37b936c27d57c

commit 670a583f75224581a26338b3c4f37b936c27d57c
Author: Mario Sanchez Prada <mario@igalia.com>
Date: Tue Sep 25 11:56:14 2018

Remove fallback URLFetcher code from DevToolsUIBindings & ShellDevToolsBindings

Remove the fallback code that still uses net::URLFetcher when the network
service feature is not enabled, since SimpleURLLoader does now work fine
either when that feature is in use or not.

This is also consistent with other migrations to SimpleURLLoader happening
all across chromium regardless of whether the network service is enabled,
and is covered by the tests that are already in place.

Bug:  840410 
Change-Id: I282f215b7892680c45d847530755f3821e353a18
Reviewed-on: https://chromium-review.googlesource.com/1238464
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#593895}
[modify] https://crrev.com/670a583f75224581a26338b3c4f37b936c27d57c/chrome/browser/devtools/devtools_ui_bindings.cc
[modify] https://crrev.com/670a583f75224581a26338b3c4f37b936c27d57c/chrome/browser/devtools/devtools_ui_bindings.h
[modify] https://crrev.com/670a583f75224581a26338b3c4f37b936c27d57c/content/shell/browser/shell_devtools_bindings.cc
[modify] https://crrev.com/670a583f75224581a26338b3c4f37b936c27d57c/content/shell/browser/shell_devtools_bindings.h

Resolving as fixed