code: function WebVrView() {
    this._width = 0;
    this._height = 0;
  
    this._proj = mat4.create();
    this._invProj = mat4.create();
  
    this._frustum = [
      vec4.create(), // left
      vec4.create(), // right
      vec4.create(), // bottom
      vec4.create(), // top
      vec4.create()  // camera
    ];
  
    this._tmpVec = vec4.create();
  }
docs: A minimal View implementation for use with WebVR.  Note that RectilinearView cannot be used because the WebVR API exposes a view matrix instead of view parameters (yaw, pitch and roll).  Most of the code has been copied verbatim from RectilinearView, but some methods are missing (e.g. screenToCoordinates and coordinatesToScreen). If we ever graduate this class to the core library, we'll need to figure out the best way to share code between the two.