WASHINGTON — China is exporting something new to the world economy: Fear. Global investors are quaking over the prospect of a devastating slump in the world’s second-biggest economy. And they’re fast losing confidence that China’s policymakers, seemingly so sure-footed in the past, know how to solve the problem. The worst-case scenario is that a collapsing Chinese economy would derail others around the world – from emerging markets in Chile and Indonesia to industrial powers such the United States, the European Union and Japan. The free-fall in the stock markets, in the words of David Kelly, chief global strategist at JP Morgan Funds, is “Made in China.” This year, the International Monetary Fund expects China’s economy to grow 6.8 percent, which would be its weakest peace since 1990. China, which was posting double-digit growth in the mid-2000s, is trying to engineer a daunting transition – from overheated growth fueled by exports and often-wasteful investment to slower growth built on consumer spending. Official numbers show the Chinese economy grew 7 percent from January through March from a year earlier.