Allow no arguments in ConstrainedHtmlUI::OnDialogClose()

chrome/browser/ui/webui/constrained_html_ui.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/constrained_html_ui.h"
 
 #include "base/lazy_instance.h"
 #include "base/values.h"
 #include "chrome/browser/ui/webui/html_dialog_ui.h"
 #include "content/browser/renderer_host/render_view_host.h"
@@ skipping 31 matching lines @@
   RegisterMessageCallback("DialogClose",
       NewCallback(this, &ConstrainedHtmlUI::OnDialogCloseMessage));
 }
 
 void ConstrainedHtmlUI::OnDialogCloseMessage(const ListValue* args) {
   ConstrainedHtmlUIDelegate* delegate = GetConstrainedDelegate();
   if (!delegate)
     return;
 
   std::string json_retval;
-  if (!args->GetString(0, &json_retval))
+  if (!args->empty() && !args->GetString(0, &json_retval))
     NOTREACHED() << "Could not read JSON argument";
   delegate->GetHtmlDialogUIDelegate()->OnDialogClosed(json_retval);
   delegate->OnDialogCloseFromWebUI();
 }
 
 ConstrainedHtmlUIDelegate*
     ConstrainedHtmlUI::GetConstrainedDelegate() {
   ConstrainedHtmlUIDelegate** property =
       GetPropertyAccessor().GetProperty(tab_contents()->property_bag());
   return property ? *property : NULL;
 }
 
 // static
 PropertyAccessor<ConstrainedHtmlUIDelegate*>&
     ConstrainedHtmlUI::GetPropertyAccessor() {
   return g_constrained_html_ui_property_accessor.Get();
 }