MacViews a11y: Support the "Show menu" action in Textfield and Combobox.

ui/accessibility/platform/ax_platform_node_mac.h

 // Copyright 2014 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_ACCESSIBILITY_AX_PLATFORM_NODE_MAC_H_
 #define UI_ACCESSIBILITY_AX_PLATFORM_NODE_MAC_H_
 
 #import <Foundation/Foundation.h>
 
 #include "base/mac/scoped_nsobject.h"
@@ skipping 23 matching lines @@
   base::scoped_nsobject<AXPlatformNodeCocoa> native_node_;
 
   DISALLOW_COPY_AND_ASSIGN(AXPlatformNodeMac);
 };
 
 }  // namespace ui
 
 AX_EXPORT
 @interface AXPlatformNodeCocoa : NSObject
 
+// Maps AX roles to native roles. Returns NSAccessibilityUnknownRole if not
+// found.
 + (NSString*)nativeRoleFromAXRole:(ui::AXRole)role;
+
+// Maps AX roles to native subroles. Returns nil if not found.
 + (NSString*)nativeSubroleFromAXRole:(ui::AXRole)role;
+
+// Maps AX events to native notifications. Returns nil if not found.
 + (NSString*)nativeNotificationFromAXEvent:(ui::AXEvent)event;
 
 - (instancetype)initWithNode:(ui::AXPlatformNodeBase*)node;
 - (void)detach;
 
 @property(nonatomic, readonly) NSRect boundsInScreen;
 @property(nonatomic, readonly) ui::AXPlatformNodeBase* node;
 
 @end
 
 #endif  // UI_ACCESSIBILITY_AX_PLATFORM_NODE_MAC_H_