Fix the issue introduced by hooking window.onbeforeunload in WebDialogView which breaks WebDialogUI…

ui/web_dialogs/web_dialog_delegate.cc

Index: ui/web_dialogs/web_dialog_delegate.cc
diff --git a/ui/web_dialogs/web_dialog_delegate.cc b/ui/web_dialogs/web_dialog_delegate.cc
index 7e920cc5cdd52df869d881a840eb880d4b53daed..ed414101abe05a217ee5a3aa99f378992a1bbec6 100644
--- a/ui/web_dialogs/web_dialog_delegate.cc
+++ b/ui/web_dialogs/web_dialog_delegate.cc
@@ -14,6 +14,11 @@ void WebDialogDelegate::GetMinimumDialogSize(gfx::Size* size) const {
   GetDialogSize(size);
 }
 
+void WebDialogDelegate::OnDialogCloseFromWebUI(
+    const std::string& json_retval) {
+  OnDialogClosed(json_retval);
+}
+
 bool WebDialogDelegate::HandleContextMenu(
     const content::ContextMenuParams& params) {
   return false;