One of the toughest calls to make, probably would have been called a goal if the refs would have went in that direction.

via the Situation Blog,

At 14:59 of the first period in the Flyers/Capitals game, the Situation Room initiated video review to further examine a play at the Philadelphia net. Video review was inconclusive in determining if Nicklas Backstrom's shot completely crossed the goal line. Therefore the referee's call on the ice stands - no goal Washington.

See the screenshot I captured and enhanced below...