The United States and its allies vowed this week to do more to counter Chinese theft of technology, warning at an unusual gathering of intelligence leaders that Beijing’s espionage is increasingly trained not on the hulking federal buildings of Washington but the shiny office complexes of Silicon Valley. The intelligence chiefs sought to engage private industry in combating what one official called an “unprecedented threat” on Tuesday as they discussed how to better protect new technologies and help Western countries keep their edge over China. The choice of meeting venue…