Open a new Chrome window with custom URL, then get that same window with Autohotkey?

I'm attempting to open up a Chrome instance with the -app flag, then move that window around and generally do stuff with it. Here's my code:

#!NumpadMult::
{
    Gui, Show , w260 h150, Window title
    Gui, Add, Edit, w100 vCustomUrl, http://
    Gui, Add, Button, default, OK  ; The label ButtonOK (if it exists) will be run when the button is pressed.

    ButtonOk:
    Gui, Submit
    Gui, Destroy
    URL = %customUrl%

    MyWidth = 639
    MyHeight = 389
    Run C:Program Files (x86)GoogleChromeApplicationchrome.exe --app=data:text/html`,<html><body><script>window.resizeTo(%MyWidth%`,%MyHeight%)`;window.location='%URL%'`;</script></body></html>

    retu
}

This is the best way I've found so far to open a Chrome window and move it around, because I can't figure out how to actually do a WinWait on a specific Chrome window for which I don't know the title. If I try to have Run spit out a pid, the pid is the same as any existing Chrome processes, so the window I get isn't necessarily the one I created.

Any ideas? I am happy to provide more information if needed.