Fix Mac accessibility window attribute inside child frames.

content/browser/accessibility/browser_accessibility_cocoa.mm

Index: content/browser/accessibility/browser_accessibility_cocoa.mm
diff --git a/content/browser/accessibility/browser_accessibility_cocoa.mm b/content/browser/accessibility/browser_accessibility_cocoa.mm
index 0ffaf1436831ab171e70f431903f1d9e30eae74f..ac975f9196ec7acb8c2c0462f5127d3e3dd5f35e 100644
--- a/content/browser/accessibility/browser_accessibility_cocoa.mm
+++ b/content/browser/accessibility/browser_accessibility_cocoa.mm
@@ -1156,9 +1156,11 @@ bool InitializeAccessibilityTreeSearch(
   } else {
     // Hook back up to RenderWidgetHostViewCocoa.
     BrowserAccessibilityManagerMac* manager =
-        static_cast<BrowserAccessibilityManagerMac*>(
-            browserAccessibility_->manager());
-    return manager->parent_view();
+        browserAccessibility_->manager()->GetRootManager()
+            ->ToBrowserAccessibilityManagerMac();
+    if (manager)
+      return manager->parent_view();
+    return nil;
   }
 }
 
@@ -1864,8 +1866,8 @@ bool InitializeAccessibilityTreeSearch(
     return nil;
 
   BrowserAccessibilityManagerMac* manager =
-      static_cast<BrowserAccessibilityManagerMac*>(
-          browserAccessibility_->manager());
+      browserAccessibility_->manager()->GetRootManager()
+          ->ToBrowserAccessibilityManagerMac();
   if (!manager || !manager->parent_view())
     return nil;