[MessageHandler] Convert the code to a proper `class`
[MessageHandler] Convert the code to a proper `class`

mozilla/pdf.js,caremerge/pdf.js,Shoobx/pdf.js,xavier114fch/pdf.js,showpad/mozilla-pdf.js,timvandermeij/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,xavier114fch/pdf.js,caremerge/pdf.js,macroplant/pdf.js,nawawi/pdf.js,nawawi/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,macroplant/pdf.js,mozilla/pdf.js,macroplant/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,mozilla/pdf.js,Snuffleupagus/pdf.js,Snuffleupagus/pdf.js