Google Inc. will cut about 4,000 jobs at its Motorola Mobility Holdings Inc. unit, or 20 percent of the staff at the company it bought for about $12.5 billion, Bloomberg reported. Two-thirds of the reductions will be outside the United States, Google said today in a regulatory filing. Google will also shut down about one-third of Motorola Mobility’s 90 facilities and simplify its wireless product portfolio, it said. Gkkoogle said the measure will incur severance-related costs of no more than $275 million. “These changes are designed to return Motorola’s mobile devices unit to profitability,” Google said in the filing.