src/vs/platform/undoRedo/common/undoRedoService.ts/EditStackSnapshot/isValid
class EditStackSnapshot:	public isValid(): boolean {
		for (let i = 0, len = this.editStacks.length; i < len; i++) {
			if (this._versionIds[i] !== this.editStacks[i].versionId) {
				return false;
			}
		}
		return true;
	}