As Treasury Secretary Janet Yellen meets Chinese Vice Premier He Lifeng this week, the two sides find themselves in an economic role reversal. The U.S. economy, buoyed by consumer spending and generous government subsidies for certain industries, bounded forward this year, notching 4.9% growth in the third quarter and defying forecasts of a recession. China, meanwhile, is mired in a property slump that has weighed down its entire economy, raising questions among economists about whether Beijing’s growth engine is permanently downshifting. The comparative U.S. strength and Chinese weakness is a change from previous rounds of diplomacy between the world’s two…