Chrome for Android does not support extensions, so we must load TouchStadia into the browser manually! Here's a tutorial video you can use to supplement the instructions below.
Open the snippet URL on your phone in Chrome (this works on regular Chrome). I recommend going to the link every time as updates will only be available there.
Select all the text in the box, and copy it.
Open Stadia and make sure to select the "Desktop site" option so it launches properly.
Hit the ENTER key on your keyboard. Stadia should recognise that a joystick was connected.
Enjoy! You must repeat this procedure if you or your browser closes or refreshes Stadia.
Simply install the extension and open or refresh Stadia! Click the extension icon to show configuration options.
To move buttons around, press CTRL+; in Stadia and layout mode will be activated (indicated by a magenta background.) Tap/click and drag buttons to change their positions during this time. Press CTRL+; again to disable layout mode. This hotkey will not work when Stadia is in-game. This is a known issue, so to ensure function please only use this shortcut outside of games for now. Layout mode is only supported on desktop currently.
Keep in mind that once you change the position of a button in layout mode, that button will no longer move relative to the window border when resizing your browser, so you must maintain the same browser window size for the layout to look consistent. If you create a layout, then shrink your browser, it's possible to lose buttons outside the visible area! To reset the layout, press the Reset button in the TouchStadia configuration.
TouchStadia also has manifest permissions to run on html5gamepad.com, where you can test the input of the controller with visual feedback! This is useful if you'd rather not wait for a game to open!
Thanks to /u/revnort for creating the amazing vector images used for the on-screen buttons and sticks!
Thanks to /u/-sxp- for creating the controller mapping fix code snippet that inspired this extension!