src/vs/workbench/services/workingCopy/common/workingCopyHistoryTracker.ts/WorkingCopyHistoryTracker/shouldTrackHistoryFromSaveEvent
class WorkingCopyHistoryTracker:	private shouldTrackHistoryFromSaveEvent(e: IWorkingCopySaveEvent): e is IStoredFileWorkingCopySaveEvent<IStoredFileWorkingCopyModel> {
		if (!isStoredFileWorkingCopySaveEvent(e)) {
			return false; // only support working copies that are backed by stored files
		}

		return this.shouldTrackHistory(e.workingCopy.resource, e.stat);
	}