Additional checks/calls for cases when WebUI may be already gone but OOBE screen instance is not

chrome/browser/ui/webui/chromeos/login/network_screen_handler.cc

 // Copyright (c) 2012 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/chromeos/login/network_screen_handler.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
@@ skipping 29 matching lines @@
 
 // NetworkScreenHandler, public: -----------------------------------------------
 
 NetworkScreenHandler::NetworkScreenHandler()
     : screen_(NULL),
       is_continue_enabled_(false),
       show_on_init_(false) {
 }
 
 NetworkScreenHandler::~NetworkScreenHandler() {
+  if (screen_)
+    screen_->OnActorDestroyed(this);
 }
 
 // NetworkScreenHandler, NetworkScreenActor implementation: --------------------
 
 void NetworkScreenHandler::SetDelegate(NetworkScreenActor::Delegate* screen) {
   screen_ = screen;
 }
 
 void NetworkScreenHandler::PrepareToShow() {
 }
@@ skipping 84 matching lines @@
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback(kJsApiNetworkOnInputMethodChanged,
       base::Bind(&NetworkScreenHandler::HandleOnInputMethodChanged,
                  base::Unretained(this)));
 }
 
 // NetworkScreenHandler, private: ----------------------------------------------
 
 void NetworkScreenHandler::HandleOnExit(const ListValue* args) {
   ClearErrors();
-  screen_->OnContinuePressed();
+  if (screen_)
+    screen_->OnContinuePressed();
 }
 
 void NetworkScreenHandler::HandleOnLanguageChanged(const ListValue* args) {
   DCHECK(args->GetSize() == 1);
   std::string locale;
   if (!args->GetString(0, &locale))
     NOTREACHED();
 
   // TODO(altimofeev): make language change async.
   LanguageSwitchMenu::SwitchLanguageAndEnableKeyboardLayouts(locale);
@@ skipping 64 matching lines @@
         "title",
         util->GetInputMethodLongName(input_methods->at(i)));
     input_method->SetBoolean("selected",
         ime_id == current_input_method_id);
     input_methods_list->Append(input_method);
   }
   return input_methods_list;
 }
 
 }  // namespace chromeos