MacViews: Fix combobox keyboard shortcuts.

ui/views/controls/combobox/combobox.h

 // 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.
 
 #ifndef UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_
 #define UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
@@ skipping 18 matching lines @@
 class ComboboxListener;
 class CustomButton;
 class MenuRunner;
 class Painter;
 class PrefixSelector;
 
 // A non-editable combobox (aka a drop-down list or selector).
 // Combobox has two distinct parts, the drop down arrow and the text. Combobox
 // offers two distinct behaviors:
 // * STYLE_NORMAL: typical combobox, clicking on the text and/or button shows
-// the drop down, arrow keys change selection, selected index can be changed by
-// the user to something other than the first item.
+//   the drop down, arrow keys change selection or show the menu depending on
+//   the platform, selected index can be changed by the user to something other
+//   than the first item.
 // * STYLE_ACTION: clicking on the text notifies the listener. The menu can be
-// shown only by clicking on the arrow. The selected index is always reverted to
-// 0 after the listener is notified.
+//   shown only by clicking on the arrow, except on Mac where it can be shown
+//   through the keyboard. The selected index is always reverted to 0 after the
+//   listener is notified.
 class VIEWS_EXPORT Combobox : public View,
                               public PrefixDelegate,
                               public ButtonListener {
  public:
   // The style of the combobox.
   enum Style {
     STYLE_NORMAL,
     STYLE_ACTION,
   };
 
@@ skipping 168 matching lines @@
 
   // Used for making calbacks.
   base::WeakPtrFactory<Combobox> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Combobox);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_