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

ui/views/examples/combobox_example.cc

Index: ui/views/examples/combobox_example.cc
diff --git a/ui/views/examples/combobox_example.cc b/ui/views/examples/combobox_example.cc
index 5a26ddd0468c54ee1a30b2b2aa0e21a783eb5c79..f3923832dbf3234f240bea81c0babff930e20545 100644
--- a/ui/views/examples/combobox_example.cc
+++ b/ui/views/examples/combobox_example.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.
 
@@ -19,7 +19,7 @@ class ComboboxModelExample : public ui::ComboboxModel {
   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));
   }