You can do this using wkhtmltopdf, which you need to install and possibly add to your system path. I have got this working for other googlevis objects, where in some cases I did not need the --enable-javascript --javascript-delay
option....
output$downloadmap <- downloadHandler("mymap.pdf" ,
content = function(file) {
#print gmap googlevis R object to a html file
print(gmap, file="gmap.html")
#call to wkhtmltopdf installed on server/pc to convert html file to pdf.
#add a delay otherwise (i got an) empty plot
system("wkhtmltopdf --enable-javascript --javascript-delay 2000 gmap.html gmap.pdf")
#copy pdf file to output
file.copy("gmap.pdf", file)
#remove created files from local storage
file.remove("gmap.pdf")
file.remove("gmap.html")
}
)