When a new mother returns to Starbucks’ corporate headquarters in Seattle after maternity leave, she learns what is behind the doors mysteriously marked “Lactation Room.” Whenever she likes, she can slip away from her desk and behind those doors, sit in a plush recliner and behind curtains, and leaf through InStyle magazine as she holds a company-supplied pump to her chest, depositing her breast milk in bottles to be toted home later. But if the mothers who staff the chain’s counters want to do the same, they must barricade themselves in small restrooms intended for customers, counting the minutes left...