src/vs/workbench/services/history/browser/historyService.ts/HistoryService/ensureHistoryLoaded
class HistoryService:	private ensureHistoryLoaded(history: Array<EditorInput | 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
			if (this.editorGroupService.isReady) {
				this.loadHistory();
			} else {
				(async () => {
					await this.editorGroupService.whenReady;

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