src/vs/workbench/services/history/browser/history.ts/HistoryService/ensureHistoryLoaded
class HistoryService:	private ensureHistoryLoaded(history: Array<IEditorInput | IResourceEditorInput> | undefined): asserts history {
		if (!this.history) {

			// Until history is loaded, it is just empty
			this.history = [];

			// We want to seed history from opened editors
			// too as well as previous stored state, so we
			// need to wait for the editor groups being ready
			(async () => {
				await this.editorGroupService.whenReady;

				this.loadHistory();
			})();
		}
	}