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

ui/accessibility/platform/ax_platform_node_mac.h

Index: ui/accessibility/platform/ax_platform_node_mac.h
diff --git a/ui/accessibility/platform/ax_platform_node_mac.h b/ui/accessibility/platform/ax_platform_node_mac.h
index 26dbb0f0cdf38ea31d879dd4bd574f35db136eaf..73657fb986da21cda8618c98785e762a30ffd41a 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.h
+++ b/ui/accessibility/platform/ax_platform_node_mac.h
@@ -41,8 +41,14 @@ class AXPlatformNodeMac : public AXPlatformNodeBase {
 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;