Not quite. If you're not logged in, Google Wallet will open a popup (as opposed to a JS modal overlay), clearly identified as "
https://accounts.google.com", prompting you to enter your username and password. The username and password are never entered under the same URL bar as the 3rd party site.
If Braintree's checkout process opened a popup window, with a clear URL bar, into which the user entered their username/password, then this would not be a problem.