Bug 373621 - Make mime-type of PDF not overridable. r=bz

MozReview-Commit-ID: 8k2XorDX0z9

--HG--
extra : transplant_source : %86J%CA%F9%E6%B3%85jk%CB%E7%0AX%8C%F1y%D9%B4%95%D9

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -522,6 +522,7 @@ static const nsDefaultMimeTypeEntry defaultMimeEntries[] =
   { APPLICATION_OGG, "ogg" },
   { AUDIO_OGG, "oga" },
   { AUDIO_OGG, "opus" },
+  { APPLICATION_PDF, "pdf" },
   { VIDEO_WEBM, "webm" },
   { AUDIO_WEBM, "webm" },
 #if defined(MOZ_WMF)