Enabled pressing TAB to cycle through the Omnibox results.

chrome/browser/autocomplete/autocomplete_edit_view_gtk.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/autocomplete/autocomplete_edit_view_gtk.h"
 
 #include <gdk/gdkkeysyms.h>
 #include <gtk/gtk.h>
 
 #include <algorithm>
@@ skipping 1665 matching lines @@
 
 void AutocompleteEditViewGtk::HandleViewMoveFocus(GtkWidget* widget,
                                                   GtkDirectionType direction) {
   if (!tab_was_pressed_)
     return;
 
   // If special behavior is triggered, then stop the signal emission to
   // prevent the focus from being moved.
   bool handled = false;
 
   // Trigger Tab to search behavior only when Tab key is pressed.

[Peter Kasting, 2011/04/01 00:09:09]

You need to rework this function in a similar way to the Windows changes.

   if (model_->is_keyword_hint())
-    handled = model_->AcceptKeyword();
+    handled = model_->AcceptKeyword(true);
 
 #if GTK_CHECK_VERSION(2, 20, 0)
   if (!handled && !preedit_.empty())
     handled = true;
 #endif
 
   if (!handled && GTK_WIDGET_VISIBLE(instant_view_))
     handled = model_->CommitSuggestedText(true);
 
   if (!handled) {
@@ skipping 628 matching lines @@
   // baseline, so we need to move the |instant_view_| down to make sure it
   // has the same baseline as the |text_view_|.
   PangoLayout* layout = gtk_label_get_layout(GTK_LABEL(instant_view_));
   int height;
   pango_layout_get_size(layout, NULL, &height);
   PangoLayoutIter* iter = pango_layout_get_iter(layout);
   int baseline = pango_layout_iter_get_baseline(iter);
   pango_layout_iter_free(iter);
   g_object_set(instant_anchor_tag_, "rise", baseline - height, NULL);
 }