To enable this, the Chromium codebase had to be made multi-desktop aware (i.e., chrome::HostDesktopType parameters were added in several locations).

 

So... a bunch of methods now take chrome::HostDesktopType, but how do you get the right HostDesktopType when you need to provide one?

There are many ways:

1. If you have a Browser: take its host_desktop_type() member.
2. If you have a gfx::NativeView: use chrome::GetHostDesktopTypeForNativeView().
3. If you have a gfx::NativeWindow: use chrome::GetHostDesktopTypeForNativeWindow().
4. If you have a WebContents* w: you can use (2) passing in w->GetNativeView()  OR you might be able to get a Browser with chrome::FindBrowserWithWebContents() and use (1)
5. If all else fails and you have absolutely NO way of getting desktop context (e.g., a background extension that wants to open a new window...): you can use chrome::GetActiveDesktop() to get the type of the last user-activated Chrome desktop, but be aware that this is inherently racy (i.e., the user can switch desktops at any time) -- If you are in a test, it is OK to use GetActiveDesktop() since almost all tests run on a single desktop making GetActiveDesktop() constant.
6. You should almost never hardcode HOST_DESKTOP_TYPE_X constants.
7. If you work on Chrome OS and your code is under ash/, please use HOST_DESKTOP_TYPE_ASH (this is the same as HOST_DESKTOP_TYPE_NATIVE on Chrome OS, but not on other platforms).

Most of the methods mentioned above are found in src/chrome/browser/ui/host_desktop.h.

 

Note: If you hardcode HOST_DESKTOP_TYPE_NATIVE it will look like it's working if you're in a single-desktop environment (which most of you are), but what it will really do is: one day someone will trigger your feature from the Ash desktop (e.g., in Windows 8 Metro) and it will open a window/tab on the native desktop (invisible to the user who is immersed in the Ash environment)...