It currently seems impossible to add Google Chrome as an external web browser in Flash Builder Standalone for Mac. In this context, Eclipse only cares about "Unix executables" and not .app files.
For example, the path to Firefox on a Mac is: /Applications/Firefox.app/Contents/MacOS/firefox-bin which is only found by right-clicking and choosing 'Show Package Contents' on Firefox.app in your Applications directory.
If you try to add Google Chrome as a new external web browser, you'll have to repeat this process to navigate to /Applications/Google Chrome.app/Contents/MacOS where the 'Google Chrome' Unix exxecutable resides.
The problem is that space in the name. If you attempt to click OK in Eclipse, you'll get an error preventing you from continuing:
The location value is not a valid path name
Are there any workarounds for this so I can use Chrome as my development browser only? I did some searching and all I could come up with was this:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=297273
UPDATE: A kind and savvy Flash Builder engineer gave me a helpful tip. Note that you'll need to show hidden files in Mac, by opening Terminal and entering the following command:
defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder
Press Return to relaunch Finder. Once hidden files are shown, "You’ll find what you need in [YOUR WORKSPACE]/.metadata/.plugins/org.eclipse.core.runtime/.settings/org.eclipse.ui.browser.prefs. There’s a 'browsers' property there that defines XML for defining Eclipse’s web browsers. Add a new browser location and name and restart Flash Builder."
In this case you'd add:
<external location\="/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" name\="Google Chrome"/>\n
I can confirm that this works. Hopefully we won't have to resort to this kind of hackery on the next go around.