add mapping from macOS flavor back to mime.

widget/src/mac/nsMimeMapper.cpp

@@ -64,3 +64,26 @@ nsMimeMapperMac :: MapMimeTypeToMacOSType ( const nsString & aMimeStr )
   return format;
   
 } // MapMimeTypeToMacOSType
+
+
+//
+// MapMacOSTypeToMimeType
+//
+// Given a MacOS flavor, map this back into the Mozilla mimetype. 
+//
+void
+nsMimeMapperMac :: MapMacOSTypeToMimeType ( ResType inMacType, nsString & outMimeStr )
+{
+  switch ( inMacType ) {
+  
+    case 'TEXT': outMimeStr = kTextMime; break;
+    case 'XIF ': outMimeStr = kXIFMime; break;
+    case 'HTML': outMimeStr = kHTMLMime; break;
+    
+    default:
+      outMimeStr = "unknown";
+      //¥¥¥ need to un-hash here.
+  
+  } // case of which flavor
+
+} // MapMacOSTypeToMimeType

widget/src/mac/nsMimeMapper.h

@@ -35,6 +35,7 @@ namespace nsMimeMapperMac {
 
     // converts from mime type (eg: text/plain) to MacOS type (eg: 'TEXT').
   ResType MapMimeTypeToMacOSType ( const nsString & aMimeStr ) ;
+  void MapMacOSTypeToMimeType ( ResType inMacType, nsString & outMimeStr ) ;
 
 } // nsMimeMapperMac