Per Issue 830041, we'll be enabling users to launch 2D Chrome from standalone/AIO Daydream devices.  However if we stop here, these users will have a worse experience than smartphone Daydream users, who get to use our VR browsing experience.

As part of our brainstorming, we agreed to add a toggle option in the 2D Chrome overflow menu to launch into the VR browsing experience.  We will similarly need a way to exit VR browsing and return to 2D mode.

Assigning to Gordon for UX spec.