Fix panels being removed from PanelManager prematurely.

content/public/browser/notification_types.h

Index: content/public/browser/notification_types.h
diff --git a/content/public/browser/notification_types.h b/content/public/browser/notification_types.h
index 1d6e50352e035801e37aeb684a2c665afd99cb62..6c8aa2424c60b8a953477463a6a05f73326be8bc 100644
--- a/content/public/browser/notification_types.h
+++ b/content/public/browser/notification_types.h
@@ -351,6 +351,10 @@ enum NotificationType {
   // Note: Used only in testing.
   NOTIFICATION_RENDER_VIEW_HOST_DID_RECEIVE_DRAG_TARGET_DROP_ACK,
 
+  // Sent from RenderViewHost::OnMsgShouldCloseACK. This means handling
+  // ViewMsg_ShouldClose has been completed and result received.
+  NOTIFICATION_RENDER_VIEW_HOST_RECEIVED_ON_MSG_SHOULD_CLOSE_ACK,
+
   // Indicates a RenderWidgetHost has been hidden or restored. The source is
   // the RWH whose visibility changed, the details is a bool set to true if
   // the new state is "visible."