Alternate computation of axObjectCacheOwner to improve perf

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 2294 matching lines @@
 }
 
 Document& Document::axObjectCacheOwner() const
 {
     // FIXME(dmazzoni): Currently there's one AXObjectCache per page, owned
     // by the top document, but with --site-isolation the top document may
     // be a remote frame. As a quick fix we're making the local root the owner
     // of the AXObjectCache (http://crbug.com/510410), but the proper fix
     // will be for each Document to  have its own AXObjectCache
     // (http://crbug.com/532249).
-
+    Document* top = const_cast<Document*>(this);
     LocalFrame* frame = this->frame();
     if (!frame)
-        return *const_cast<Document*>(this);
+        return *top;
 
-    frame = frame->localFrameRoot();
-    if (!frame || !frame->document())
-        return *const_cast<Document*>(this);
-
-    Document* owner = frame->document();
-    if (frame->pagePopupOwner()) {
-        ASSERT(!owner->m_axObjectCache);
-        return frame->pagePopupOwner()->document().axObjectCacheOwner();
+    // This loop is more efficient than calling localFrameRoot.
+    while (frame && frame->owner() && frame->owner()->isLocal()) {
+        HTMLFrameOwnerElement* owner = toHTMLFrameOwnerElement(frame->owner());
+        top = &owner->document();
+        frame = top->frame();
     }
 
-    return *owner;
+    if (top->frame() && top->frame()->pagePopupOwner()) {
+        ASSERT(!top->m_axObjectCache);
+        return top->frame()->pagePopupOwner()->document().axObjectCacheOwner();
+    }
+
+    ASSERT(top);
+    return *top;
 }
 
 void Document::clearAXObjectCache()
 {
     ASSERT(&axObjectCacheOwner() == this);
     // Clear the cache member variable before calling delete because attempts
     // are made to access it during destruction.
     if (m_axObjectCache)
         m_axObjectCache->dispose();
     m_axObjectCache.clear();
@@ skipping 3537 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif