Potential fix for browser crash while ChromeVox is on.

chrome/browser/ui/aura/accessibility/automation_manager_aura.cc

 // Copyright 2014 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.
 
 #include "chrome/browser/ui/aura/accessibility/automation_manager_aura.h"
 
 #include <vector>
 
 #include "base/memory/singleton.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 132 matching lines @@
       0, /* process_id */
       0 /* routing_id */);
   std::vector<content::AXEventNotificationDetails> details;
   details.push_back(detail);
   extensions::automation_util::DispatchAccessibilityEventsToAutomation(
       details, context, gfx::Vector2d());
 }
 
 void AutomationManagerAura::OnNativeFocusChanged(aura::Window* focused_now) {
   focused_window_ = focused_now;
+  if (focused_now && !focused_now->HasObserver(this))
+    focused_now->AddObserver(this);
 }
+
+void AutomationManagerAura::OnWindowDestroying(aura::Window* window) {
+  if (focused_window_ == window) {
+    window->RemoveObserver(this);
+    focused_window_ = nullptr;
+  }
+}