More than 20 years after it redefined fast shipping, Amazon is preparing to raise the bar on consumer expectations again by offering to fulfill customers' most urgent product needs in a half-hour or less for an extra fee. The company, which revolutionized online shopping in 2005 with two-day deliveries for Prime members, is rapidly opening small order-processing hubs in dozens of U.S. and foreign cities to cater to shoppers who can't or don't want to wait for cough medicine to relieve flu symptoms or tomatoes for tonight's dinner salad. The ultrafast service, called Amazon Now, first launched in India last June. Amazon says 30-minute deliveries now are also available in urban areas of Brazil, Mexico , Japan, the United Arab Emirates, the United Kingdom and the United States. The mini-warehouses devoted to Amazon Now are about the size of a CVS drugstore.…