Seems like this would be a good fit for chrome.identity, e.g. chrome.identity.isDemoUser().

Should this query should require a permission (like "identity")? I'd argue that it should be available to all apps.

The chrome.runtime.onLaunched event already includes |isPublicSession| and |isKioskMode| -- maybe |isDemoMode| makes more sense there.

Worth noting that most Demo Mode apps will be custom-written demo apps. This API may still be useful for built-in apps like Files.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/456e84e95d9f7060c117953d251e121bc052b158

commit 456e84e95d9f7060c117953d251e121bc052b158
Author: Michael Giuffrida <michaelpg@chromium.org>
Date: Thu Jul 12 01:33:12 2018

Add isDemoSession to chrome.app.runtime LaunchData

Adds the |isDemoSession| boolean property to launch data for the
chrome.app.runtime.onLaunched event.

Built-in platform apps on Chrome OS will check this to enable special
Chrome OS Demo Mode behavior.

This CL adds the property as |false|; a follow-up CL will correctly set
it to |true| when the device is actually in Demo Mode.

Bug:  835024 
Change-Id: Ie77f50f1551c3dfb00fff27e7779775ceca1f44d
Reviewed-on: https://chromium-review.googlesource.com/1121113
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Sergey Volk <servolk@chromium.org>
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574447}
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chrome/browser/extensions/chrome_extensions_browser_client.cc
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chrome/browser/extensions/chrome_extensions_browser_client.h
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chrome/test/data/extensions/platform_apps/launch_file/test.js
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chrome/test/data/extensions/platform_apps/launch_whitelisted_ext_with_file/test.js
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chromecast/browser/extensions/cast_extensions_browser_client.cc
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/chromecast/browser/extensions/cast_extensions_browser_client.h
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/browser/api/app_runtime/app_runtime_api.cc
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/browser/extensions_browser_client.h
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/browser/test_extensions_browser_client.cc
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/browser/test_extensions_browser_client.h
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/common/api/app_runtime.idl
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/renderer/resources/app_runtime_custom_bindings.js
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/shell/browser/shell_extensions_browser_client.cc
[modify] https://crrev.com/456e84e95d9f7060c117953d251e121bc052b158/extensions/shell/browser/shell_extensions_browser_client.h