I dont think the chrome addon will work. At least other addons didnt work on chromium since the NPAPI interface is removed. I think i tested Vysor too.
When i get home from work later this week i'll try capturing the screen trough ADB with the internal screengrabber as sugested earlier in this thread. With this no addon is needed and i think we can set the resolution and framerate via the command line. This will require the shield to be connected to the rpi with usb.