GTK: Now that we depend on gtk 2.18+, replace this pattern:

chrome/browser/ui/gtk/tabs/tab_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/ui/gtk/tabs/tab_gtk.h"
 
 #include <gdk/gdkkeysyms.h>
 
 #include "base/memory/singleton.h"
 #include "base/utf_string_conversions.h"
@@ skipping 222 matching lines @@
 
 bool TabGtk::IsSelected() const {
   return delegate_->IsTabSelected(this);
 }
 
 bool TabGtk::IsVisible() const {
   return GTK_WIDGET_FLAGS(event_box_) & GTK_VISIBLE;
 }
 
 void TabGtk::SetVisible(bool visible) const {
-  if (visible) {
-    gtk_widget_show(event_box_);
-  } else {
-    gtk_widget_hide(event_box_);
-  }
+  gtk_widget_set_visible(event_box_, visible);
 }
 
 void TabGtk::CloseButtonClicked() {
   delegate_->CloseTab(this);
 }
 
 void TabGtk::UpdateData(TabContents* contents, bool app, bool loading_only) {
   TabRendererGtk::UpdateData(contents, app, loading_only);
   // Cache the title width so we don't recalculate it every time the tab is
   // resized.
@@ skipping 67 matching lines @@
     gdk_event_free(last_mouse_down_);
     last_mouse_down_ = NULL;
   }
 
   // Notify the drag helper that we're done with any potential drag operations.
   // Clean up the drag helper, which is re-created on the next mouse press.
   delegate_->EndDrag(canceled);
 
   observer_.reset();
 }