One accessibility tree per frame.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 232 matching lines @@
     function(*this);
 
     for (Frame* child = m_frame->tree().firstChild(); child; child = child->tree().nextSibling()) {
         if (!child->isLocalFrame())
             continue;
         if (FrameView* childView = toLocalFrame(child)->view())
             childView->forAllNonThrottledFrameViews(function);
     }
 }
 
-void FrameView::removeFromAXObjectCache()
-{
-    if (AXObjectCache* cache = axObjectCache())
-        cache->childrenChanged(m_frame->pagePopupOwner());
-}
-
 void FrameView::init()
 {
     reset();
 
     m_size = LayoutSize();
 
     // Propagate the marginwidth/height and scrolling modes to the view.
     if (m_frame->owner() && m_frame->owner()->scrollingMode() == ScrollbarAlwaysOff)
         setCanHaveScrollbars(false);
 }
 
 void FrameView::dispose()
 {
     RELEASE_ASSERT(!isInPerformLayout());
 
     if (ScrollAnimatorBase* scrollAnimator = existingScrollAnimator())
         scrollAnimator->cancelAnimation();
     cancelProgrammaticScrollAnimation();
 
     detachScrollbars();
 
-    // When the view is no longer associated with a frame, it needs to be removed from the ax object cache
-    // right now, otherwise it won't be able to reach the topDocument()'s axObject cache later.
-    removeFromAXObjectCache();
-
     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
         scrollingCoordinator->willDestroyScrollableArea(this);
 
     // Destroy |m_autoSizeInfo| as early as possible, to avoid dereferencing
     // partially destroyed |this| via |m_autoSizeInfo->m_frameView|.
     m_autoSizeInfo.clear();
 
     if (m_postLayoutTasksTimer.isActive())
         m_postLayoutTasksTimer.stop();
 
@@ skipping 3820 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink