Add download item tooltips on linux/win.

chrome/browser/gtk/download_item_gtk.h

Index: chrome/browser/gtk/download_item_gtk.h
diff --git a/chrome/browser/gtk/download_item_gtk.h b/chrome/browser/gtk/download_item_gtk.h
index e2abcb97aef718bfe70c9f58e353174cfc2b5d17..fbe2ec575e40bba1a268bf49f066e3fe96334e32 100644
--- a/chrome/browser/gtk/download_item_gtk.h
+++ b/chrome/browser/gtk/download_item_gtk.h
@@ -76,6 +76,9 @@ class DownloadItemGtk : public DownloadItem::Observer,
   // Ask the icon manager to asynchronously start loading the icon for the file.
   void LoadIcon();
 
+  // Sets the tooltip on the download button.
+  void UpdateTooltip();
+
   // Sets the name label to the correct color.
   void UpdateNameLabel();