GTK: make more use of gtk_signal convenience macros/signal registrar.

chrome/browser/gtk/tab_contents_drag_source.h

Index: chrome/browser/gtk/tab_contents_drag_source.h
diff --git a/chrome/browser/gtk/tab_contents_drag_source.h b/chrome/browser/gtk/tab_contents_drag_source.h
index f43629ffb9fc6ee5f01d5e46585f46fcc5316d36..d11e4e1579be34cb224d7e5790cd2c85c9ffa33c 100644
--- a/chrome/browser/gtk/tab_contents_drag_source.h
+++ b/chrome/browser/gtk/tab_contents_drag_source.h
@@ -90,11 +90,11 @@ class TabContentsDragSource : public MessageLoopForUI::Observer {
   // The URL to download from for a drag-out download.
   GURL download_url_;
 
-  // The widget that provides visual feedback for the drag. We use this instead
-  // of gtk_drag_set_icon_pixbuf() because some window managers will use shadows
-  // or other visual effects on top level windows.
+  // The widget that provides visual feedback for the drag.
   GtkWidget* drag_icon_;
 
+  GtkSignalRegistrar signals_;
+
   DISALLOW_COPY_AND_ASSIGN(TabContentsDragSource);
 };