Specifically http://trac.webkit.org/browser/trunk/WebCore/platform/graphics/FontFastPath.cpp?rev=57215 causes use to go down the complex font path for Latin and Greek diacritics. Looks like our complex font path for Lucida Grande breaks on Windows. The ḿ gets the unrecognized character block. I tested on a local Safari build and it does not have this problem, so I think it must be possible to get this right. I hacked it locally to use GDI since Safari doesn't use GDI for Lucida Grande.
LayoutTest failures for Chromium are being marked WontFix. The Bug is still accessible and referenced from TestExpectations.