Chevron Corp. of San Ramon is drawing harsh criticism for its business ties to Burma, the Asian nation conducting a brutal military crackdown. The company owns part of a natural gas project in Burma, where soldiers crushed pro-democracy protests last week and killed at least 10 people. U.S. sanctions prevent most U.S. companies from working in Burma, but Chevron?s investment there existed before the sanctions were imposed and continues under a grandfather clause. As a result, the company is one of the few large Western companies left in the country.