IAccessible::get_accChild should only return a descendant.

ui/accessibility/platform/ax_platform_node_base.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 "ui/accessibility/platform/ax_platform_node_base.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/accessibility/platform/ax_platform_node_delegate.h"
 
@@ skipping 75 matching lines @@
     return FromNativeViewAccessible(parent->ChildAtIndex(next_index));
   return nullptr;
 }
 
 bool AXPlatformNodeBase::IsDescendant(AXPlatformNodeBase* node) {
   CHECK(delegate_);
   if (!node)
     return false;
   if (node == this)
     return true;
-  AXPlatformNodeBase* parent = FromNativeViewAccessible(node->GetParent());
+  gfx::NativeViewAccessible native_parent = node->GetParent();
+  if (!native_parent)
+    return false;
+  AXPlatformNodeBase* parent = FromNativeViewAccessible(native_parent);
   return IsDescendant(parent);
 }
 
 bool AXPlatformNodeBase::HasBoolAttribute(
     ui::AXBoolAttribute attribute) const {
   CHECK(delegate_);
   return GetData().HasBoolAttribute(attribute);
 }
 
 bool AXPlatformNodeBase::GetBoolAttribute(
@@ skipping 82 matching lines @@
 }
 
 // static
 AXPlatformNodeBase* AXPlatformNodeBase::FromNativeViewAccessible(
     gfx::NativeViewAccessible accessible) {
   return static_cast<AXPlatformNodeBase*>(
       AXPlatformNode::FromNativeViewAccessible(accessible));
 }
 
 }  // namespace ui