Instructions to run WebXR without headset

This doc has instructions to run Chrome with a mock OpenVR component,
which can be useful for reproing some WebXR bugs, especially if you
don't have a headset.

Change-Id: I0b7081aea3b5da58367a4ae97124fc70b6a254cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1754642
Commit-Queue: Jacob DeWitt <jacde@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687052}

docs/README.md

@@ -374,6 +374,10 @@ used when committed.
 *   [Mojo “Style” Guide](security/mojo.md) - Recommendations for best practices
     from Mojo and IPC reviewers
 
+### WebXR
+*   [Running OpenVR Without Headset](xr/run_openvr_without_headset.md) -
+    Instructions for running OpenVR on Windows without a headset
+
 ### Probably Obsolete
 *   [TPM Quick Reference](tpm_quick_ref.md) - Trusted Platform Module notes.
 *   [System Hardening Features](system_hardening_features.md) - A list of

docs/xr/run_openvr_without_headset.md

@@ -0,0 +1,31 @@
+# Running OpenVR without a headset
+
+On Windows, you can use a mock OpenVR component to run some basic WebXR
+functionality in Chrome without connecting a VR headset. This can be useful for
+reproing and investigating WebXR bugs without as much setup required.
+
+Replace `out\debug` with wherever your build output is going.
+This assumes Chrome checkout is in `c:\src\chromium\src`
+
+1. Build the mock openvr:
+```shell
+autoninja -C out\debug openvr_mock
+```
+
+2. Set environment variables so we use the mock openvr
+```shell
+set VR_OVERRIDE=C:\src\chromium\src\out\debug\mock_vr_clients\
+set VR_CONFIG_PATH=C:\src\chromium\src\out\debug
+set VR_LOG_PATH=C:\src\chromium\src\out\debug
+```
+
+3. Run Chrome with WebXR and OpenVR enabled, but WMR disabled.
+```shell
+out\debug\chrome.exe --enable-features="WebXR,OpenVR" --disable-features="WindowsMixedReality"
+```
+
+4. Navigate to a test page, by going to this [index](https://storage.googleapis.com/chromium-webxr-test/index.html)
+   clicking the link for the latest revision, and then navigating to the
+   appropriate page, such as xr-barebones.html.
+
+5. Click "Enter XR" to start an XR session that uses the mock OpenVR component.