Uses the activedescendant_changed event received from Blink to fire the right focus event

content/browser/accessibility/browser_accessibility_manager.cc

 // 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.
 
 #include "content/browser/accessibility/browser_accessibility_manager.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "build/build_config.h"
@@ skipping 434 matching lines @@
     ancestor = ancestor->GetParent();
   }
 
   // The "scrolled to anchor" notification is a great way to get a
   // screen reader to jump directly to a specific location in a document.
   NotifyAccessibilityEvent(ui::AX_EVENT_SCROLLED_TO_ANCHOR, node);
 }
 
 BrowserAccessibility* BrowserAccessibilityManager::GetActiveDescendantFocus(
     BrowserAccessibility* focus) {
-  if (!focus)
-    return NULL;
+  if (!focus || !focus->instance_active())

[dmazzoni, 2016/04/18 18:27:03]

We shouldn't ever have to check instance_active() here.

The only time we need to check instance_active is in the implementation of a
native API function, like get_accChild, etc.

When instance_active() is false, we've already removed all references to the
object, it's completely unreachable - the only remaining references are held by
another process.

+    return nullptr;
 
-  int active_descendant_id;
+  int32_t active_descendant_id;
   if (focus->GetIntAttribute(ui::AX_ATTR_ACTIVEDESCENDANT_ID,
                              &active_descendant_id)) {
     BrowserAccessibility* active_descendant =
         focus->manager()->GetFromID(active_descendant_id);
     if (active_descendant)
       return active_descendant;
   }
   return focus;
 }
 
@@ skipping 380 matching lines @@
       tree_source(tree_->CreateTreeSource());
   ui::AXTreeSerializer<const ui::AXNode*,
                        ui::AXNodeData,
                        ui::AXTreeData> serializer(tree_source.get());
   ui::AXTreeUpdate update;
   serializer.SerializeChanges(tree_->root(), &update);
   return update;
 }
 
 }  // namespace content