process(inputs, meta, callback) {
    this.enqueue_({
      inputs: inputs,
      meta: meta,
      callback: callback,
    });
    this.dispatch_();
  }
Run operation on input data.
@param {Array<ImageData>} inputs Array of image data.
@param {Object} meta A user data object.  This is passed to all operations
    and must be serializable.
@param {function(Error, ImageData, Object): void} callback Called when work
    completes.  The first argument is any error.  The second is the ImageData
    generated by operations.  The third is the user data object.