Make extension callbacks with auto-dismissing dialogs

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h

Index: chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h
diff --git a/chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h b/chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h
index 1417cd780aa9759bd9798ef3321d93b47a173153..57daac7e855d294950b519ae721a730851b1ea3d 100644
--- a/chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h
+++ b/chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h
@@ -91,6 +91,9 @@ class JavaScriptDialogTabHelper
   content::JavaScriptDialogType dialog_type_ =
       content::JavaScriptDialogType::JAVASCRIPT_DIALOG_TYPE_ALERT;
 
+  // The WebContents that was marked as showing the dialog.
+  content::WebContents* alerting_web_contents_ = nullptr;
+
   // The callback provided for when the dialog is closed. Usually the dialog
   // itself calls it, but in the cases where the dialog is closed not by the
   // user's input but by a call to |CloseDialog|, this class will call it.