Bug 891334 - Add default MIME type definition for .pdf as 'application/pdf'. r=jdm

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -465,6 +465,7 @@ static nsExtraMimeTypeEntry extraMimeEntries [] =
   { "application/x-arj", "arj", "ARJ file" },
   { "application/rtf", "rtf", "Rich Text Format File" },
   { APPLICATION_XPINSTALL, "xpi", "XPInstall Install" },
+  { APPLICATION_PDF, "pdf", "Portable Document Format" },
   { APPLICATION_POSTSCRIPT, "ps,eps,ai", "Postscript File" },
   { APPLICATION_XJAVASCRIPT, "js", "Javascript Source File" },
   { APPLICATION_XJAVASCRIPT, "jsm", "Javascript Module Source File" },