Bug 301152: Don't corrupt Cocoa scrollbars that change during redraw. r=josh r=cl sr=smfr a=jay

widget/src/cocoa/nsNativeScrollbar.mm

@@ -500,7 +500,7 @@ nsNativeScrollbar::UpdateScroller()
   BOOL enableScrollbar = (mIsEnabled && (mMaxValue > 0));
   [scrollbarView setEnabled:enableScrollbar];
   
-  [scrollbarView setNeedsDisplay:YES];
+  Invalidate(FALSE);
 }