Chrome Version       : 62.0.3202.94
OS Version: Debian 9.1

What steps will reproduce the problem?
1. launch chrome (stable) with --enable-experimental-extension-apis
2. load extension which uses chrome.app.window.create(... { alphaEnabled: true });
3. launch extension

What is the expected result?
A window with a background with alpha enabled

What happens instead of that?
Window does not get created, instead an error is printed in console:

Unchecked runtime.lastError while running app.window.create: The alphaEnabled option requires dev channel or newer.

UserAgentString: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Safari/537.36

Attached is the chrome app. 

According to https://bugs.chromium.org/p/chromium/issues/detail?id=763960 the --enable-experimental-extension-apis flag should bypass any channel restrictions. The alpha restriction is still enforced, even with this flag enabled.

 

Deleted: Screenshot from 2017-12-08 13-42-01.png 27.8 KB

	Screenshot from 2017-12-08 13-42-01.png 27.8 KB View Download

Deleted: Screenshot from 2017-12-08 13-42-15.png 128 KB

	Screenshot from 2017-12-08 13-42-15.png 128 KB View Download

Deleted: transparent-chrome-app.zip 2.1 KB

transparent-chrome-app.zip 2.1 KB Download