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

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index ecfcc9ca472deff504ac837d80ceea708b2370b3..f918d1320043865700e576de13764d527da4925b 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -1561,6 +1561,10 @@ gfx::Point RenderWidgetHostViewMac::AccessibilityOriginInScreen(
   return gfx::Point(originInScreen.x, originInScreen.y);
 }
 
+NSView* RenderWidgetHostViewMac::AccessibilityGetAcceleratedWidget() {
+  return cocoa_view_;
+}
+
 void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
   if (active) {
     if (GetTextInputType() == ui::TEXT_INPUT_TYPE_PASSWORD)