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

ui/views/examples/combobox_example.cc

-// 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.
 
 #include "ui/views/examples/combobox_example.h"
 
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
 #include "ui/base/models/combobox_model.h"
 #include "ui/views/controls/combobox/combobox.h"
 #include "ui/views/layout/fill_layout.h"
 
 namespace {
 
 // An sample combobox model that generates list of "Item <index>".
 class ComboboxModelExample : public ui::ComboboxModel {
  public:
   ComboboxModelExample() {}
   virtual ~ComboboxModelExample() {}
 
   // Overridden from ui::ComboboxModel:
-  virtual int GetItemCount() OVERRIDE { return 10; }
+  virtual int GetItemCount() const OVERRIDE { return 10; }
   virtual string16 GetItemAt(int index) OVERRIDE {
     return UTF8ToUTF16(base::StringPrintf("Item %d", index));
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ComboboxModelExample);
 };
 
 }  // namespace
 
@@ skipping 17 matching lines @@
 
 void ComboboxExample::ItemChanged(Combobox* combo_box,
                                   int prev_index,
                                   int new_index) {
   PrintStatus("Selected: index=%d, label=%s",
       new_index, UTF16ToUTF8(combo_box->model()->GetItemAt(new_index)).c_str());
 }
 
 }  // namespace examples
 }  // namespace views