Iron Man has become the golden boy for Marvel Studios, becoming the first picture of the year to cross the $300-million mark at the domestic box office. According to Music by Numbers, the film had grossed $299.3 million through Tuesday and was a sure bet to blow past $300 million on Wednesday or today (Thursday). Three films grossed more than $300 million in 2007: Spider-Man 3 ($336.5 million); Shrek the Third ($322.7 million), and Pirates of the Caribbean: At World's End ($309.4 million).