content/services/isolated_xr_device/README.md
For a more thorough/high level overview of the entire WebXR stack, please refer to components/webxr.
Chromium's WebXR implementation makes use of the multiprocess architecture for added security. Thus all code which directly interfaces with and talks to the XR hardware ("runtimes") ends up loaded/hosted in a separate XR Utility process, except on Android where it runs in-process within the browser process (primarily to ensure access to and manipulation of Android SurfaceViews for rendering, and secondarily to minimize process overhead).
The XrDeviceService serves as the entry point for the VRServiceImpl in
content/browser/xr to talk to this process, while the
IsolatedXRRuntimeProvider is the main in-process entry point. The runtime
provider continually polls for supported runtimes and, when a change is
detected, creates and returns the appropriate runtime over Mojo. The Mojo
interfaces used by this process are defined in device/vr.
To support browser tests without coupling production service definitions to
test-only Mojom, XRDeviceService::BindHookForTesting accepts a type-erased
mojo::ScopedMessagePipeHandle and forwards it to device::OpenXrPlatformHelper::BindHookForTesting.
In test targets, this pipe is unwrapped by the static test hook registrar and
bound to OpenXrTestHelper. See
//chrome/browser/vr/test/xr_browser_tests.md
and //device/vr/public/mojom/test/README.md
for complete details.