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

ui/views/focus/focus_traversal_unittest.cc

Index: ui/views/focus/focus_traversal_unittest.cc
diff --git a/ui/views/focus/focus_traversal_unittest.cc b/ui/views/focus/focus_traversal_unittest.cc
index f0ef1f4b59774d1914b12aae31427364580da9f0..471f7aa80cc4212992708fbfe2f8f818c8eae167 100644
--- a/ui/views/focus/focus_traversal_unittest.cc
+++ b/ui/views/focus/focus_traversal_unittest.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.
 
@@ -88,9 +88,9 @@ const int kThumbnailSuperStarID = count++;
 
 class DummyComboboxModel : public ui::ComboboxModel {
  public:
-  virtual int GetItemCount() { return 10; }
-
-  virtual string16 GetItemAt(int index) {
+  // Overridden from ui::ComboboxModel:
+  virtual int GetItemCount() const OVERRIDE { return 10; }
+  virtual string16 GetItemAt(int index) OVERRIDE {
     return ASCIIToUTF16("Item ") + base::IntToString16(index);
   }
 };