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

content/browser/renderer_host/render_widget_host_view_mac.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 #include <IOSurface/IOSurface.h>
 #include <stddef.h>
@@ skipping 290 matching lines @@
   void BeginFrameSubscription(
       std::unique_ptr<RenderWidgetHostViewFrameSubscriber> subscriber) override;
   void EndFrameSubscription() override;
   ui::AcceleratedWidgetMac* GetAcceleratedWidgetMac() const override;
   void OnSwapCompositorFrame(uint32_t output_surface_id,
                              cc::CompositorFrame frame) override;
   void ClearCompositorFrame() override;
   BrowserAccessibilityManager* CreateBrowserAccessibilityManager(
       BrowserAccessibilityDelegate* delegate, bool for_root_frame) override;
   gfx::Point AccessibilityOriginInScreen(const gfx::Rect& bounds) override;
+  gfx::AcceleratedWidget AccessibilityGetAcceleratedWidget() override;
 
   bool HasAcceleratedSurface(const gfx::Size& desired_size) override;
   gfx::Rect GetBoundsInRootWindow() override;
   void LockCompositingSurface() override;
   void UnlockCompositingSurface() override;
 
   bool LockMouse() override;
   void UnlockMouse() override;
   void GestureEventAck(const blink::WebGestureEvent& event,
                        InputEventAckState ack_result) override;
@@ skipping 219 matching lines @@
 
   // Factory used to safely scope delayed calls to ShutdownHost().
   base::WeakPtrFactory<RenderWidgetHostViewMac> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewMac);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_