I also tried adding the following preference:
"'extensions.ui.developer_mode': true" but it also didn't work. In case it was not clear, this is triggered by using Selenium + Chromedriver 2.33.

The 'Chrome is being controlled by automated test software' infobar is what led me to want to disable it using by not using the 'enable-automation' switch...which led to the annoying alert. This all started when I had to update Selenium and Chromedriver after Chrome 62 was updated/installed on my machine.

The issue seems to be out of TE-scope as it is related to selenium using chromedriver. 
Hence, adding label TE-NeedsTriageHelp for further investigation from dev team.

Thanks...!!

The purpose of 'enable-automation' flag is to allow Chrome to load an automation extension that is useful to ChromeDriver. Displaying "Chrome is being controlled by automated test software" is just a side effect, definitely not its main purpose. If you need to remove this flag, please also tell ChromeDriver not to load the automation extension. The syntax differs by the language API. As an example, in Python you need

options = webdriver.ChromeOptions()
options.add_experimental_option('useAutomationExtension', False)
driver = webdriver.Chrome(chrome_options=options)

Thanks for the update, John! I think what testing automation users are out there experiencing is this (please bear with me):
They are running automated tests and there is an Infobar displaying that "Chrome is being controlled by automated test software", and that's annoying them.
They google around to figure out how to get rid of it and they find articles like this (https://sqa.stackexchange.com/questions/26051/chrome-driver-2-28-chrome-is-being-controlled-by-automated-test-software-noti) saying to use the 'disable-infobars' switch.
This may work, but it seems like maybe it would also prevent the Infobar from displaying useful information some day that doesn't have to do with "Chrome is being controlled by automated test software".
Chromedriver's own capabilities page (https://sites.google.com/a/chromium.org/chromedriver/capabilities) and others points to Peter Beverloo's page (https://peter.sh/experiments/chromium-command-line-switches/) as the resource to use to learn about flags/switches.
The 'disable-infobars' switch says that it "Prevent infobars from appearing", which suggests there are other types of infobars than the automated test warning one, so I'm trying to find a more "correct" solution to the direct problem whereas using "disable-infobars" seems a bit ham-handed.
That same Peter Beverloo document states that 'enable-automation' has the following description: 'Inform users that their browser is being controlled by an automated test'.

So if you're saying that the 'enable-automation' flag is doing more than that description, then we're definitely in agreement! Seems like this description should be updated regardless of whether anyone agrees this is something that should be changed.

But furthermore, a resourceful user pointed me to this issue (https://codereview.chromium.org/2564973002) which is seemingly responsible for adding the infobar in question when 'enable-automation' is set, but it also states that at the same time "It also disables the developer mode extensions
warning bubble.". This seems to be where the "issue" stems from: the coupled enablement of the infobar and disablement of the extensions mode warning (and vice-versa) based on the 'enable-automation' switch.

It seems to me that there ought to be a way to disable this particular infobar while still disabling the extensions mode warning.

Is there any way to accomplish this currently? I'd be happy to spread the word!

...and I'll check, but I don't think that not loading the Automation Extension is an option since it's needed to perform automation, is it not?

I just did try setting the 'useAutomationExtension' ChromeOption to false to see what happens. Chrome still seems to be able to be communicated with via Selenium, however I have to assume that certain functions must be not possible or compromised.

John's comment earlier said that the extension is "an automation extension that is useful to ChromeDriver." Is there any documentation of what, more specifically, this extension enables?

Python sample code:

from selenium import webdriver

driver = webdriver.Remote(
	command_executor='http://localhost:4444/wd/hub',
	desired_capabilities={
		'browserName': 'chrome',
		'goog:chromeOptions': {
			'binary':'/path/to/Chrome65/binary',
			'excludeSwitches': ['enable-automation'],
			'useAutomationExtension': False}
		}
	)