preload blockly on idle (#4170)
preload blockly on idle (#4170)


switchinnovations/pxt,Microsoft/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,playi/pxt,switchinnovations/pxt,playi/pxt,switchinnovations/pxt,switch-education/pxt,playi/pxt,switch-education/pxt,switch-education/pxt,switchinnovations/pxt,Microsoft/pxt,playi/pxt,Microsoft/pxt