WebUI: prevent WebContent to hold invalid pointer.

chrome/browser/ui/webui/constrained_web_dialog_ui.cc

Index: chrome/browser/ui/webui/constrained_web_dialog_ui.cc
diff --git a/chrome/browser/ui/webui/constrained_web_dialog_ui.cc b/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
index 08a533067e37084f8b166a90db0443e24d1751bf..5ab3cb4cad4ef4869284d9018b45e94af7fe9a1e 100644
--- a/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
+++ b/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
@@ -108,6 +108,12 @@ void ConstrainedWebDialogUI::SetConstrainedDelegate(
                             new ConstrainedWebDialogDelegateUserData(delegate));
 }
 
+// static
+void ConstrainedWebDialogUI::ClearConstrainedDelegate(
+    content::WebContents* web_contents) {
+  web_contents->RemoveUserData(&kConstrainedWebDialogDelegateUserDataKey);
+}
+
 ConstrainedWebDialogDelegate* ConstrainedWebDialogUI::GetConstrainedDelegate() {
   ConstrainedWebDialogDelegateUserData* user_data =
       static_cast<ConstrainedWebDialogDelegateUserData*>(