I wouldn't bump old threads if you can, this thread is now out of date. Since this thread, Construct 2 has gained built-in support for the Gamepad API and Chrome 21 has been released with support for gamepads on by default - you don't need to change anything in chrome://flags.
Unfortunately that means if it doesn't work then your gamepad is not recognised... possibly file a bug at crbug.com and see if Google can fix it.