Don't call AcceptCurrentInstantPreview() when the user hits Tab.

chrome/browser/ui/gtk/omnibox/omnibox_view_gtk.cc

 // Copyright 2012 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/ui/gtk/omnibox/omnibox_view_gtk.h"
 
 #include <gdk/gdkkeysyms.h>
 #include <gtk/gtk.h>
 
 #include <algorithm>
@@ skipping 1522 matching lines @@
 
     handled = true;
   }
 
   if (supports_pre_edit_ && !handled && !pre_edit_.empty())
     handled = true;
 
   if (!handled && gtk_widget_get_visible(instant_view_))
     handled = model()->CommitSuggestedText(true);
 
-  if (!handled)
-    handled = model()->AcceptCurrentInstantPreview();
-
   if (handled) {
     static guint signal_id = g_signal_lookup("move-focus", GTK_TYPE_WIDGET);
     g_signal_stop_emission(widget, signal_id, 0);
   }
 }
 
 void OmniboxViewGtk::HandleCopyClipboard(GtkWidget* sender) {
   HandleCopyOrCutClipboard(true);
 }
 
@@ skipping 588 matching lines @@
 void OmniboxViewGtk::AdjustVerticalAlignmentOfInstantView() {
   // By default, GtkTextView layouts an anchored child widget just above the
   // 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);
   int baseline = pango_layout_get_baseline(layout);
   g_object_set(instant_anchor_tag_, "rise", baseline - height, NULL);
 }