ASCOT, England, June 18 : Star stayer Scandinavia chased down last year's winner Trawlerman in the dying stages to claim the Gold Cup at Royal Ascot and land trainer Aidan O'Brien his 100th winner at flat racing's most prestigious festival.   Locked in a neck-and-neck battle to the finish with long-term leader Trawlerman, Scandinavia showed grit and bravery to snatch the race under Ryan Moore on the line. Trawlerman broke well, galloping strongly ahead of Scandinavia and Caballo de Mar and led