WRs Stevie, Brandon on 49ers' bubble?

The San Francisco 49ers have plenty of veteran depth in their WR corps but little in the way of sure-fire playmakers. Michael Crabtree and Anquan Boldin top the depth chart, but Crabtree will have to stay healthy and Boldin is aging. And if offseason additions Stevie Johnson and Brandon Lloyd are unable to secure the No. 3 role, they may not even make the final cut.