The most successful film of 1954 was the lighthearted extravaganza “White Christmas,” which created a thin plot about four singer-dancers hired to perform at a Vermont snow lodge, only to find no snow and no guests. The main purpose of the story, finally brought to the stage 50 years later, is to allow plenty of room for a cornucopia of Irving Berlin songs, including classic tunes like “Blue Skies,” “Let Yourself Go,” and “Let Me Sing and I’m Happy,” as well as songs specifically written for the 1954 film, including “Count Your Blessings,” “Sisters,” and “Snow.”