Use BrowserAccessibilityComWin::Destroy to clear delegate and owner.

content/browser/accessibility/browser_accessibility_com_win.h

 // Copyright (c) 2017 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_ACCESSIBILITY_BROWSER_ACCESSIBILITY_COM_WIN_H_
 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_COM_WIN_H_
 
 #include <atlbase.h>
 #include <atlcom.h>
 #include <oleacc.h>
@@ skipping 727 matching lines @@
   }
   std::vector<int32_t>& hyperlinks() const {
     return win_attributes_->hyperlinks;
   }
 
  private:
   // Setter and getter for the browser accessibility owner
   BrowserAccessibilityWin* GetOwner() const { return owner_; }
   void SetOwner(BrowserAccessibilityWin* owner) { owner_ = owner; }
 
+  // Called when BrowserAccessibilityWin is about to go away.
+  // At this point, we detach from it.
+  void detach() {

[dmazzoni, 2017/05/10 06:15:50]

I think this is the same as AXPlatformNode::Destroy(), can't you override that?

I'm fine with renaming it Detach() or Release()

+    owner_ = nullptr;
+    delegate_ = nullptr;
+  }
+
   BrowserAccessibilityManager* owners_manager() const;
 
   // Returns the IA2 text attributes for this object.
   std::vector<base::string16> ComputeTextAttributes() const;
 
   // Add one to the reference count and return the same object. Always
   // use this method when returning a BrowserAccessibilityComWin object as
   // an output parameter to a COM interface, never use it otherwise.
   BrowserAccessibilityComWin* NewReference();
 
@@ skipping 215 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityComWin);
 };
 
 CONTENT_EXPORT BrowserAccessibilityComWin* ToBrowserAccessibilityComWin(
     BrowserAccessibility* obj);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_COM_WIN_H_