Once the patch is committed, this can be reproduced by replacing the definition of WebXrControllerInputOpenVRMock in webxr_vr_input_browser_test.cc with the following:

class WebXrControllerInputOpenVRMock : public MockOpenVRDeviceHookBase {
 public:
  void WaitGetControllerData(
      unsigned int index,
      device_test::mojom::XRTestHook::WaitGetControllerDataCallback callback) final;

  void ToggleTrigger(unsigned int index,
                     device::ControllerFrameData& controller_data) {
    uint64_t trigger_mask = vr::ButtonMaskFromId(vr::k_EButton_SteamVR_Trigger);
    controller_data.packet_number++;
    controller_data.buttons_pressed ^= trigger_mask;
    UpdateController(index, controller_data);
    // Wait until the updated state has been picked up by OpenVR.
    DCHECK(!wait_loop_);
    wait_loop_ = new base::RunLoop(base::RunLoop::Type::kNestableTasksAllowed);
    num_times_polled_ = 0;
    wait_loop_->Run();
    delete wait_loop_;
    wait_loop_ = nullptr;
  }

  void PressReleaseTrigger(unsigned int index,
                           device::ControllerFrameData& controller_data) {
    ToggleTrigger(index, controller_data);
    ToggleTrigger(index, controller_data);
  }

 private:
  base::RunLoop* wait_loop_ = nullptr;
  unsigned int num_times_polled_ = 0;
};

void WebXrControllerInputOpenVRMock::WaitGetControllerData(
    unsigned int index,
    device_test::mojom::XRTestHook::WaitGetControllerDataCallback callback) {
  MockOpenVRDeviceHookBase::WaitGetControllerData(index, std::move(callback));
  if (wait_loop_) {
    num_times_polled_++;
    // 5 consistent but slow (~10 seconds)
    // 6 can fail
    // 7 faster than 5, but still slow (~7 seconds)
    // 8 about the same (~7 seconds)
    // 9 slow again, can also fail (~8 seconds)
    // 10 kinda slow (~6 seconds)
    if (num_times_polled_ == 8) {
      wait_loop_->Quit();
    }
  }
}