getProjectionMatrix() {
    if (this.vrDisplay && this.vrDisplay.getFrameData) {
      if (!frameData) {
        frameData = new VRFrameData();
      }
      this.vrDisplay.getFrameData(frameData);

      // Can use either left or right projection matrix
      return frameData.leftProjectionMatrix;
    }
    return null;
  }
Gets the projection matrix from AR-enabled VRDisplay
if possible.
@return {!Float32Array}