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

content/browser/accessibility/browser_accessibility.cc

Index: content/browser/accessibility/browser_accessibility.cc
diff --git a/content/browser/accessibility/browser_accessibility.cc b/content/browser/accessibility/browser_accessibility.cc
index 93d7828694f1e5f49489346d889fa9e7cf4fa216..bead70f80cbb592797d21544549e7090ecdc925f 100644
--- a/content/browser/accessibility/browser_accessibility.cc
+++ b/content/browser/accessibility/browser_accessibility.cc
@@ -131,10 +131,9 @@
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetChild(
     uint32_t child_index) const {
-  DCHECK_LT(child_index, PlatformChildCount());
   BrowserAccessibility* result = nullptr;
 
-  if (HasIntAttribute(ui::AX_ATTR_CHILD_TREE_ID)) {
+  if (child_index == 0 && HasIntAttribute(ui::AX_ATTR_CHILD_TREE_ID)) {
     BrowserAccessibilityManager* child_manager =
         BrowserAccessibilityManager::FromID(
             GetIntAttribute(ui::AX_ATTR_CHILD_TREE_ID));