Enable DumpAccessibilityTree tests to use cross-process iframes.

content/browser/accessibility/browser_accessibility_manager.cc

Index: content/browser/accessibility/browser_accessibility_manager.cc
diff --git a/content/browser/accessibility/browser_accessibility_manager.cc b/content/browser/accessibility/browser_accessibility_manager.cc
index 8979f10f0f0580792be6d7300938c28f31b5babf..75c0b821589fd4c547be0fa412253e53f458b6b8 100644
--- a/content/browser/accessibility/browser_accessibility_manager.cc
+++ b/content/browser/accessibility/browser_accessibility_manager.cc
@@ -614,16 +614,23 @@ void BrowserAccessibilityManager::OnAtomicUpdateFinished(
   }
 }
 
-BrowserAccessibilityDelegate*
-    BrowserAccessibilityManager::GetDelegateFromRootManager() {
+BrowserAccessibilityManager* BrowserAccessibilityManager::GetRootManager() {
   if (!GetRoot())
     return nullptr;
   int parent_tree_id = GetTreeData().parent_tree_id;
   BrowserAccessibilityManager* parent_manager =
       BrowserAccessibilityManager::FromID(parent_tree_id);
   if (parent_manager)
-    return parent_manager->GetDelegateFromRootManager();
-  return delegate();
+    return parent_manager->GetRootManager();
+  return this;
+}
+
+BrowserAccessibilityDelegate*
+    BrowserAccessibilityManager::GetDelegateFromRootManager() {
+  BrowserAccessibilityManager* root_manager = GetRootManager();
+  if (root_manager)
+    return root_manager->delegate();
+  return nullptr;
 }
 
 ui::AXTreeUpdate