In a major piece of stock market news, Abigail Johnson, 52 years old, was named Monday as chief executive officer of FMR, the parent company of Fidelity Investments, and also of Fidelity itself, according to a memorandum distributed to employees of the Boston-based financial services behemoth and to company spokesman Vin Loporchio. The firm was founded by her grandfather in 1946. Her father, Edward C.