layer's framebuffer and blit the multisampled framebuffer over to it.
          gl.bindFramebuffer(gl.READ_FRAMEBUFFER, this.multisampleFramebuffer);
          gl.bindFramebuffer(gl.DRAW_FRAMEBUFFER, layer.framebuffer);

          gl.blitFramebuffer(0, 0, this.renderbufferWidth, this.renderbufferHeight,
                             0, 0, this.renderbufferWidth, this.renderbufferHeight,
                             gl.COLOR_BUFFER_BIT, gl.LINEAR);
        }
      };

      let app = new CustomWebXRSampleApp(