ui/base/models: Make ComboboxModel::GetItemCount() a constant function.

chrome/browser/bookmarks/recently_used_folders_combo_model.cc

Index: chrome/browser/bookmarks/recently_used_folders_combo_model.cc
diff --git a/chrome/browser/bookmarks/recently_used_folders_combo_model.cc b/chrome/browser/bookmarks/recently_used_folders_combo_model.cc
index ecf2dfeaee56e37e5da1b3d3c5470865364902c6..0e6dfe31e2faa8867d7fce5f06338cad0c1209ed 100644
--- a/chrome/browser/bookmarks/recently_used_folders_combo_model.cc
+++ b/chrome/browser/bookmarks/recently_used_folders_combo_model.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 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.
 
@@ -54,7 +54,7 @@ RecentlyUsedFoldersComboModel::RecentlyUsedFoldersComboModel(
 
 RecentlyUsedFoldersComboModel::~RecentlyUsedFoldersComboModel() {}
 
-int RecentlyUsedFoldersComboModel::GetItemCount() {
+int RecentlyUsedFoldersComboModel::GetItemCount() const {
   return static_cast<int>(nodes_.size() + 1);
 }