Support exp.json::loading.backgroundImageUrl
Support exp.json::loading.backgroundImageUrl

fbshipit-source-id: ac28aa5

exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,jolicloud/exponent,exponentjs/exponent,jolicloud/exponent,jolicloud/exponent,jolicloud/exponent,exponent/exponent,jolicloud/exponent,exponent/exponent,jolicloud/exponent,exponentjs/exponent,exponent/exponent,jolicloud/exponent,jolicloud/exponent,exponentjs/exponent,exponentjs/exponent,jolicloud/exponent