CL at https://chromium-review.googlesource.com/c/chromium/src/+/770138

I think the current behavior is more-or-less correct - we want this on dev channel, since that's where it's been consistently.  It would also be nice to have this on > dev channel by opt-in.

I think the desired option is to disable it on dev channel?

#4 I'm flexible :)

Yeah the main goal would be to be able to explicitly disable it on any channel. Granted this would only be important on the dev channel currently, but if the default changes on other channels, I'd still want to be able to disable it on those channels. 

I think the ideal is what the chrome://flags normally do with choices of (Enable, Disable, Default). So that we can control it explicitly when desired. The Default would be enable on <= dev and disable on > dev.

WDYT?

Yep, that sounds reasonable to me.  All this should really need, I think, is changing ErrorConsole::IsEnabledForChromeExtensionsPage() to be:

bool ErrorConsole::IsEnabledForChromeExtensionsPage() const {
  if (!profile_->GetPrefs()->GetBoolean(prefs::kExtensionsUIDeveloperMode))
    return false;  // Only enabled in developer mode.

  // If the user specified a command line switch (either for enabling or disabling),
  // respect that.
  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kErrorConsole))
    return FeatureSwitch::error_console()->IsEnabled();

  // Enable by default on dev channel, disabled on other channels.
  return GetCurrentChannel() <= version_info::Channel::DEV;
}

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b

commit ea8d15b6adaebdfd55db396b6623c8c27acf3f0b
Author: Dave Schuyler <dschuyler@chromium.org>
Date: Thu Nov 16 01:11:49 2017

[MD extensions] command line control of error-console

This CL makes the extensions error console page able to be enabled/disabled
using --enable-error-console and --disable-error-console command line switches.

Bug:  785062 
Change-Id: I4906be4effdc4b5c8a97451a1cb64688b8cbe699
Reviewed-on: https://chromium-review.googlesource.com/770138
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516933}
[modify] https://crrev.com/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b/chrome/browser/extensions/error_console/error_console.cc
[modify] https://crrev.com/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b/chrome/browser/extensions/error_console/error_console.h
[modify] https://crrev.com/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b/chrome/browser/extensions/error_console/error_console_unittest.cc
[modify] https://crrev.com/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b/extensions/common/feature_switch.cc
[modify] https://crrev.com/ea8d15b6adaebdfd55db396b6623c8c27acf3f0b/extensions/common/feature_switch.h