On the Mac, AX_EVENT_LOAD_COMPLETE should only be fired on the top document.

content/browser/accessibility/browser_accessibility_manager_mac.mm

 // 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 "content/browser/accessibility/browser_accessibility_manager_mac.h"
 
 #import "base/mac/mac_util.h"
 #import "base/mac/sdk_forward_declarations.h"
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 173 matching lines @@
     case ui::AX_EVENT_AUTOCORRECTION_OCCURED:
       mac_notification = NSAccessibilityAutocorrectionOccurredNotification;
       break;
     case ui::AX_EVENT_FOCUS:
       mac_notification = NSAccessibilityFocusedUIElementChangedNotification;
       break;
     case ui::AX_EVENT_LAYOUT_COMPLETE:
       mac_notification = NSAccessibilityLayoutCompleteNotification;
       break;
     case ui::AX_EVENT_LOAD_COMPLETE:
-      mac_notification = NSAccessibilityLoadCompleteNotification;
+      // This notification should only be fired on the top document.
+      // Iframes should use |AX_EVENT_LAYOUT_COMPLETE| to signify that they have
+      // finished loading.
+      if (IsRootTree()) {
+        mac_notification = NSAccessibilityLoadCompleteNotification;
+      } else {
+        mac_notification = NSAccessibilityLayoutCompleteNotification;
+      }
       break;
     case ui::AX_EVENT_INVALID_STATUS_CHANGED:
       mac_notification = NSAccessibilityInvalidStatusChangedNotification;
       break;
     case ui::AX_EVENT_SELECTED_CHILDREN_CHANGED:
       if (node->GetRole() == ui::AX_ROLE_GRID ||
           node->GetRole() == ui::AX_ROLE_TABLE) {
         mac_notification = NSAccessibilitySelectedRowsChangedNotification;
       } else {
         mac_notification = NSAccessibilitySelectedChildrenChangedNotification;
@@ skipping 260 matching lines @@
   }
 
   return @{
     NSAccessibilityTextStateChangeTypeKey : @(AXTextStateChangeTypeEdit),
     NSAccessibilityTextChangeValues : changes,
     NSAccessibilityTextChangeElement : native_node
   };
 }
 
 }  // namespace content