Bug 276431 moved nsSVGUtils::ConvertToSurfaceSize from the .cpp file to the .h file, so that it can be called from imagelib in non-libxul builds: http://hg.mozilla.org/mozilla-central/annotate/827cba9e2671/layout/svg/base/src/nsSVGUtils.h#l425 Once we move to a libxul-only world, that method can & should move back to the .cpp file.
This was done in bug 649429, but I can't dupe it because I can't access that bug. Could you?
Thanks for pointing that out. Resolving as FIXED with a dependency on that bug. (Not duping since the main thrust of that bug was completely different from this.) The checkin from that bug that fixed this was: http://hg.mozilla.org/mozilla-central/rev/33b198be1aa3