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

content/browser/accessibility/browser_accessibility_manager_win.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_win.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <vector>
@@ skipping 118 matching lines @@
 
 void BrowserAccessibilityManagerWin::OnIAccessible2Used() {
   BrowserAccessibilityStateImpl::GetInstance()->OnScreenReaderDetected();
 }
 
 void BrowserAccessibilityManagerWin::UserIsReloading() {
   if (GetRoot())
     MaybeCallNotifyWinEvent(IA2_EVENT_DOCUMENT_RELOAD, GetRoot());
 }
 
+BrowserAccessibility* BrowserAccessibilityManagerWin::GetFocus() {
+  BrowserAccessibility* node = BrowserAccessibilityManager::GetFocus();
+
+  // Combo boxes have an invisible list inside them which tracks the active list

[dmazzoni, 2016/04/29 20:55:54]

Isn't the combo box itself supposed to have activedescendant on it?

Either way, consider moving this to cross-platform code, because we should track
the activedescendant of a combobox on all platforms. If there's something
platform-specific, it should maybe just be a tiny override on Mac that says not
to follow active descendant focus on Mac because it doesn't work that way

+  // item.
+  if (node && node->GetRole() == ui::AX_ROLE_COMBO_BOX) {

[dmazzoni, 2016/04/29 20:55:54]

Same here, only if combo box is editable?

+    BrowserAccessibility* child = node->InternalGetChild(0);
+    if (child && child->GetRole() == ui::AX_ROLE_LIST) {
+      BrowserAccessibility* active_list_item = GetActiveDescendantFocus(child);
+      if (active_list_item != child)
+        return active_list_item;
+    }
+  }
+
+  return GetActiveDescendantFocus(node);
+}
+
 void BrowserAccessibilityManagerWin::NotifyAccessibilityEvent(
     ui::AXEvent event_type,
     BrowserAccessibility* node) {
+  DCHECK(node);
   BrowserAccessibilityDelegate* root_delegate = GetDelegateFromRootManager();
   if (!root_delegate || !root_delegate->AccessibilityGetAcceleratedWidget()) {
     DLOG(WARNING) << "Not firing AX event because of no root_delegate or hwnd";
     return;
   }
 
   // Don't fire events when this document might be stale as the user has
   // started navigating to a new document.
   if (user_is_navigating_away_)
     return;
 
   // Inline text boxes are an internal implementation detail, we don't
   // expose them to Windows.
   if (node->GetRole() == ui::AX_ROLE_INLINE_TEXT_BOX)
     return;
 
   LONG event_id = EVENT_MIN;
   switch (event_type) {
-    case ui::AX_EVENT_ACTIVEDESCENDANTCHANGED:
+    case ui::AX_EVENT_ACTIVEDESCENDANTCHANGED: {
       event_id = IA2_EVENT_ACTIVE_DESCENDANT_CHANGED;
       break;
+    }
     case ui::AX_EVENT_ALERT:
       event_id = EVENT_SYSTEM_ALERT;
       break;
     case ui::AX_EVENT_AUTOCORRECTION_OCCURED:
       event_id = IA2_EVENT_OBJECT_ATTRIBUTE_CHANGED;
       break;
     case ui::AX_EVENT_BLUR:
       // Equivalent to focus on the root.
       event_id = EVENT_OBJECT_FOCUS;
       node = GetRoot();
@@ skipping 29 matching lines @@
         node = focus_object;
       event_id = IA2_EVENT_TEXT_CARET_MOVED;
       break;
     }
     default:
       // Not all WebKit accessibility events result in a Windows
       // accessibility notification.
       break;
   }
 
-  if (!node)
-    return;
-
   if (event_id != EVENT_MIN)
     MaybeCallNotifyWinEvent(event_id, node);
 
   // If this is a layout complete notification (sent when a container scrolls)
   // and there is a descendant tracked object, send a notification on it.
   // TODO(dmazzoni): remove once http://crbug.com/113483 is fixed.
   if (event_type == ui::AX_EVENT_LAYOUT_COMPLETE &&
       tracked_scroll_object_ &&
       tracked_scroll_object_->IsDescendantOf(node)) {
     MaybeCallNotifyWinEvent(
         IA2_EVENT_VISIBLE_DATA_CHANGED, tracked_scroll_object_);
     tracked_scroll_object_->Release();
     tracked_scroll_object_ = NULL;
   }
 }
 
 bool BrowserAccessibilityManagerWin::CanFireEvents() {
   BrowserAccessibilityDelegate* root_delegate = GetDelegateFromRootManager();
   if (!root_delegate)
     return false;
   HWND hwnd = root_delegate->AccessibilityGetAcceleratedWidget();
   return hwnd != nullptr;
 }
 
 void BrowserAccessibilityManagerWin::FireFocusEvent(
     BrowserAccessibility* node) {
+  DCHECK(node);
   // On Windows, we always fire a FOCUS event on the root of a frame before
   // firing a focus event within that frame.
   if (node->manager() != last_focused_manager_ &&
       node != node->manager()->GetRoot()) {
     NotifyAccessibilityEvent(ui::AX_EVENT_FOCUS, node->manager()->GetRoot());
   }
 
   BrowserAccessibilityManager::FireFocusEvent(node);
 }
 
@@ skipping 75 matching lines @@
 
 void BrowserAccessibilityManagerWin::TrackScrollingObject(
     BrowserAccessibilityWin* node) {
   if (tracked_scroll_object_)
     tracked_scroll_object_->Release();
   tracked_scroll_object_ = node;
   tracked_scroll_object_->AddRef();
 }
 
 }  // namespace content