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

content/browser/accessibility/browser_accessibility_manager.cc

Index: content/browser/accessibility/browser_accessibility_manager.cc
diff --git a/content/browser/accessibility/browser_accessibility_manager.cc b/content/browser/accessibility/browser_accessibility_manager.cc
index 3564fe2f8ffc01893ae49dad5233d179009d97d4..f02dc9c8a8ecae9ddc2b2759ca3b5c229fa56e91 100644
--- a/content/browser/accessibility/browser_accessibility_manager.cc
+++ b/content/browser/accessibility/browser_accessibility_manager.cc
@@ -1032,6 +1032,10 @@ BrowserAccessibilityDelegate*
   return nullptr;
 }
 
+bool BrowserAccessibilityManager::IsRootTree() {
+  return delegate() && delegate()->AccessibilityGetAcceleratedWidget();
+}
+
 ui::AXTreeUpdate
 BrowserAccessibilityManager::SnapshotAXTreeForTesting() {
   std::unique_ptr<