SAN FRANCISCO — A federal appeals court on Friday upheld former Giants slugger Barry Bonds' obstruction-of-justice conviction stemming from rambling testimony he gave during a 2003 appearance before a grand jury investigating elite athletes' use of performance-enhancing drugs. The 9th U.S. Circuit Court of Appeals ruled that Bonds' testimony was "evasive" and capable of misleading investigators and hindering their probe into a performance-enhancing-drug ring centered at the Bay Area Laboratory Co-Operative, better known as BALCO. Like several other prominent athletes who testified before the grand jury, Bonds was granted immunity from criminal prosecution as long as he testified truthfully. But after Bonds repeatedly denied knowingly using performance-enhancing drugs — he testified he thought he was taking flax seed oil and other legal supplements — prosecutors charged him with obstruction and with making false statements.