Fix accessibility with out-of-process iframes.

content/browser/accessibility/browser_accessibility.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.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 42 matching lines @@
     case ui::AX_ROLE_SLIDER:
     case ui::AX_ROLE_STATIC_TEXT:
     case ui::AX_ROLE_TEXT_FIELD:
       return true;
     default:
       return false;
   }
 }
 
 uint32 BrowserAccessibility::PlatformChildCount() const {
+  if (HasBoolAttribute(ui::AX_ATTR_IS_AX_TREE_HOST))

[dmazzoni, 2015/06/25 22:15:38]

Not due to your change, but let's change this to GetBoolAttribute instead.
HasBoolAttribute happens to work correctly because we prune attributes whose
value is false, 0, or "" but GetBoolAttribute would be more correct.

More important, though: this needs to call
manager_->delegate()->AccessibilityGetChildFrame and only return 1 if the child
currently exists. It will be common for a parent frame to have a child frame ID
when the child frame isn't loaded yet. If someone calls PlatformChildCount() and
then iterates over the children immediately afterwards from the same thread, it
shouldn't ever get NULL.

[lfg, 2015/06/25 22:48:24]

Done. I also changed the DCHECK below to call this function, since the condition
became more complex.

+    return 1;
+
   return PlatformIsLeaf() ? 0 : InternalChildCount();
 }
 
 bool BrowserAccessibility::IsNative() const {
   return false;
 }
 
 bool BrowserAccessibility::IsDescendantOf(
     BrowserAccessibility* ancestor) {
   if (this == ancestor) {
     return true;
   } else if (GetParent()) {
     return GetParent()->IsDescendantOf(ancestor);
   }
 
   return false;
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetChild(
     uint32 child_index) const {
-  DCHECK(child_index < InternalChildCount());
-  BrowserAccessibility* result = InternalGetChild(child_index);
+  DCHECK((child_index == 0 && HasBoolAttribute(ui::AX_ATTR_IS_AX_TREE_HOST)) ||
+         child_index < InternalChildCount());
+  BrowserAccessibility* result = nullptr;
 
-  if (result->HasBoolAttribute(ui::AX_ATTR_IS_AX_TREE_HOST)) {
+  if (HasBoolAttribute(ui::AX_ATTR_IS_AX_TREE_HOST)) {
     BrowserAccessibilityManager* child_manager =
-        manager_->delegate()->AccessibilityGetChildFrame(result->GetId());
+        manager_->delegate()->AccessibilityGetChildFrame(GetId());
     if (child_manager)
       result = child_manager->GetRoot();
+  } else {
+    result = InternalGetChild(child_index);
   }
 
   return result;
 }
 
 bool BrowserAccessibility::PlatformIsChildOfLeaf() const {
   BrowserAccessibility* ancestor = GetParent();
   while (ancestor) {
     if (ancestor->PlatformIsLeaf())
       return true;
@@ skipping 42 matching lines @@
     return manager_->GetFromAXNode(parent);
 
   if (!manager_->delegate())
     return NULL;
 
   BrowserAccessibility* host_node =
       manager_->delegate()->AccessibilityGetParentFrame();
   if (!host_node)
     return NULL;
 
-  return host_node->GetParent();
+  return host_node;
 }
 
 int32 BrowserAccessibility::GetIndexInParent() const {
   return node_ ? node_->index_in_parent() : -1;
 }
 
 int32 BrowserAccessibility::GetId() const {
   return node_ ? node_->id() : -1;
 }
 
@@ skipping 592 matching lines @@
       }
       need_to_offset_web_area = true;
     }
     parent = parent->GetParentForBoundsCalculation();
   }
 
   return bounds;
 }
 
 }  // namespace content