async getArtifact(context) {
    const eventProcessPromises = context.dependencies.Scripts
      .filter(script => script.sourceMapURL)
      .map(script => this._retrieveMapFromScript(context.driver, script));
    return Promise.all(eventProcessPromises);
  }
@param {LH.Gatherer.Context<'Scripts'>} context
@return {Promise<LH.Artifacts['SourceMaps']>}