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

ui/views/controls/combobox/native_combobox_views_unittest.cc

 // 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 "base/utf_string_conversions.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 #include "ui/base/models/combobox_model.h"
 #include "ui/views/controls/combobox/combobox.h"
 #include "ui/views/controls/combobox/native_combobox_views.h"
 #include "ui/views/ime/mock_input_method.h"
@@ skipping 32 matching lines @@
     key_received_ = key_handled_ = false;
   }
 
  private:
   bool key_handled_;
   bool key_received_;
 
   DISALLOW_COPY_AND_ASSIGN(TestCombobox);
 };
 
-// A concrete class is needed to test the combobox
+// A concrete class is needed to test the combo box.
 class TestComboboxModel : public ui::ComboboxModel {
  public:
   TestComboboxModel() {}
   virtual ~TestComboboxModel() {}
-  virtual int GetItemCount() {
+
+  // Overridden from ui::ComboboxModel:
+  virtual int GetItemCount() const OVERRIDE {
     return 4;
   }
-  virtual string16 GetItemAt(int index) {
-    EXPECT_GE(index, 0);
-    EXPECT_LT(index, GetItemCount());
+  virtual string16 GetItemAt(int index) OVERRIDE {
     return string16();
   }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(TestComboboxModel);
 };
 
 }  // namespace
 
 namespace views {
 
 class NativeComboboxViewsTest : public ViewsTestBase {
  public:
@@ skipping 105 matching lines @@
   widget_->SetContentsView(container);
   container->AddChildView(combobox_);
 
   combobox_view_ = static_cast<NativeComboboxViews*>(
       combobox_->GetNativeWrapperForTesting());
   ASSERT_TRUE(combobox_view_);
   ASSERT_FALSE(combobox_view_->enabled());
 }
 
 }  // namespace views