Walgreens, the giant drugstore chain, announced on Wednesday that it will keep its headquarters in the Chicago area instead of claiming an overseas corporate home in Switzerland in order to lower its tax bill.  But  a growing number of other U.S. companies have completed or are considering a tax dodge known as inversions. Pfizer and Chiquita are part of what the non-partisan Congressional Research Service called a new wave of inversions that are raising concerns about an erosion of the U.S. tax base. The practice has come in for criticism from Sen. Bernie Sanders. “Corporate deserters,” he called companies that use the loophole to siphon off tax revenue from the United States. He proposed legislation to yank government contracts from businesses that set up addresses in foreign tax havens. Already, one in four U.S. corporations use tax havens like the Cayman Islands to avoid paying any U.S. income tax at all.