Driveby-sharing: Chrome doesn't work on pure image files (jpg/png/...).

[seul]

It doesn't work here: http://25.media.tumblr.com/tumblr_m5m5339Sga1qza249o1_400.jpg
And neither on some other jpg I tried
Nor on this .png: http://gritttt-rss.nicolashoening.de/style/logo.png

[seul]

How to reproduce:
In chromium

• Go to one of the above links
• click the drive by bookmarklet
• Overlay doesn't show – no error, nothing.

[nhoening]

The line

head.appendChild(css);

throws this error:

Uncaught TypeError: Cannot call method 'appendChild' of undefined

Reason is tat there is no HTML structure in an image to append our CSS to. Firefox has an implicit HTML structure, it seems. I don't know how best fix this. At least we should check if head is defined, of course, but I am unsure if sharing images will work (nicely) on Chrome.