Bug 161333 js perf improvement in msgMail3PaneWindow.js, GetFirstSelectedMessage() r=dmose sr=sspitzer

mailnews/base/resources/content/msgMail3PaneWindow.js

@@ -1237,19 +1237,7 @@ function GetSelectedMsgFolders()
 function GetFirstSelectedMessage()
 {
     try {
-        // Use this instead of gDBView.URIForFirstSelectedMessage, else it
-        // will return the currentIndex message instead of the highlighted
-        // message.
-        //
-        // note, there may not be any selected messages
-        //
-        // XXX todo
-        // is this inefficient when we've got a lot of message selected?
-        var selectedMessages = GetSelectedMessages();
-        if (selectedMessages)
-          return selectedMessages[0];
-        else
-          return null;
+        return gDBView.URIForFirstSelectedMessage;
     }
     catch (ex) {
         return null;

mailnews/base/src/nsMsgDBView.cpp

@@ -5344,13 +5344,14 @@ nsMsgDBView::GetKeyForFirstSelectedMessage(nsMsgKey *key)
     return NS_OK;
   }
 
-  PRInt32 currentIndex;
-  nsresult rv = mTreeSelection->GetCurrentIndex(&currentIndex);
+  PRInt32 startRange;
+  PRInt32 endRange;
+  nsresult rv = mTreeSelection->GetRangeAt(0, &startRange, &endRange);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // check that the first index is valid, it may not be if nothing is selected
-  if (currentIndex >= 0 && currentIndex < GetSize()) {
-    *key = m_keys.GetAt(currentIndex);
+  if (startRange >= 0 && startRange < GetSize()) {
+    *key = m_keys.GetAt(startRange);
   }
   else {
     return NS_ERROR_UNEXPECTED;