Currently, the WebVR implementation requires a user gesture in order to present (which is in line with the spec). This makes it impossible to do automated testing using Clank/Chrome proper. ContentShell has a way of faking user gestures, but that isn't a complete solution unless we want to run all WebVR related tests in ContentShell.

Adding a runtime flag is probably the simplest way to achieve this, similar to how we have a runtime flag to enable the "Enter VR" option in the overflow menu for testing purposes.