Washington (AFP) – Google announced plans Wednesday to limit ad tracking on its Android operating system running on billions of devices, a sensitive privacy issue that rival Apple has already moved to address on its iPhones. Tech giants are under growing pressure to better balance privacy and ad-targeting, as users complain and regulators threaten tougher rules — but the companies themselves try to maintain access to the precious data helping them earn billions in ad revenue. Apple has about 50 percent of the US smartphone market while Google’s Android software is used on roughly 85 percent …