We may end up moving such methods off of the main XR runtime device objects to simplify those - both initialization and scope. For example, arcore_device.cc includes a lot of additional headers just to handle permissions.

Removing Blink>WebVR component and assigning to Blink>WebXR 

Removing Blink>WebVR component and assigning to Blink>WebXR 

Related discussion from a CR comment.  https://chromium-review.googlesource.com/#/c/1256217/9/device/vr/public/mojom/isolated_xr_service.mojom@80

We could add another interface XRSessionProvider that is obtained from XRRuntime when we check the runtime is up to date, and request updates/install modules.

Currently we have XRRuntime that exposes several methods, and we have some assumptions (which we validate) about order that methods are called in.  Specifically that EnsureInitialized() is called before RequestSession().

By chaining a few interfaces/methods, the type system will guarantee ordering is what we expect.

XRRuntime::EnsureInitialized() -> (XRSessionProvider)
XRSessionProvider::RequestSession(options) -> (XRSession, XRSessionController)

Additionally, this cleanup will naturally fit with allowing the browser to order version checks and permission checks correctly in sequence before requesting a session from a runtime.

We may want to implement the changes for "AR mode" first since that could affect the flow.