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to help.

What steps will reproduce the problem?
Launch a webdriver.Chrome with chrome_options and desired_capabilities.  In particular,
include a *subkey* in desired_capabilities, like desired_capabilities["chromeOptions"]["excludeSwitches"]

What is the expected output? What do you see instead?

I would expect Chrome to be launched respecting the subkey passed to chromeOptions.

When the chrome_options are merged into the desired_capabilities, subkeys are instead
overwritten, because it is a shallow dictionary update, not a deep merge.

Specifically, any value specified in desired_capabilities["chromeOptions"]["excludeSwitches"]
is overwritten when a new Options().to_capabilities is merged on top, overwriting the
whole chromeOptions subkey

For more detail, see script.py here: https://gist.github.com/jasonm/b5e3f58203eb253204f7

I think a fix to this file:
https://code.google.com/p/selenium/source/browse/py/selenium/webdriver/chrome/webdriver.py

Would look something like these lines:
https://gist.github.com/jasonm/b5e3f58203eb253204f7#file-selenium-webdriver-chrome-webdriver-py-L47-L57

Selenium version: python selenium 2.42.0
OS: Mac OS
Browser: Chrome
Browser version: 35

Please provide any additional information below. A sample reduced test
case, or a public URL that demonstrates the problem will intrigue our merry
band of Open Source developers far more than nothing at all: they'll be far
more likely to look at your problem if you make it easy for them!