Fix AppModalDialogHelper to deal with a TabStrip without an active tab

chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm

 // 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/cocoa/javascript_app_modal_dialog_cocoa.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
@@ skipping 206 matching lines @@
 }
 
 @end
 
 ////////////////////////////////////////////////////////////////////////////////
 // JavaScriptAppModalDialogCocoa, public:
 
 JavaScriptAppModalDialogCocoa::JavaScriptAppModalDialogCocoa(
     app_modal::JavaScriptAppModalDialog* dialog)
     : dialog_(dialog),
-      popup_helper_(new AppModalDialogHelper(dialog->web_contents())),
+      popup_helper_(
+          new AppModalDialogHelper(dialog ? dialog->web_contents() : NULL)),

[Bernhard Bauer, 2014/12/22 13:18:35]

nullptr

[Bernhard Bauer, 2014/12/22 13:18:35]

Also, instead of doing this `dialog ? dialog->web_contents() : nullptr` thing
everywhere, why don't you just pass the JavaScriptAppModalDialog* in?

       is_showing_(false) {
   // Determine the names of the dialog buttons based on the flags. "Default"
   // is the OK button. "Other" is the cancel button. We don't use the
   // "Alternate" button in NSRunAlertPanel.
   NSString* default_button = l10n_util::GetNSStringWithFixup(IDS_APP_OK);
   NSString* other_button = l10n_util::GetNSStringWithFixup(IDS_APP_CANCEL);
   bool text_field = false;
   bool one_button = false;
   switch (dialog_->javascript_message_type()) {

[Bernhard Bauer, 2014/12/22 13:18:35]

|dialog_| might be NULL here.

     case content::JAVASCRIPT_MESSAGE_TYPE_ALERT:
       one_button = true;
       break;
     case content::JAVASCRIPT_MESSAGE_TYPE_CONFIRM:
       if (dialog_->is_before_unload_dialog()) {
         if (dialog_->is_reload()) {
           default_button = l10n_util::GetNSStringWithFixup(
               IDS_BEFORERELOAD_MESSAGEBOX_OK_BUTTON_LABEL);
           other_button = l10n_util::GetNSStringWithFixup(
               IDS_BEFORERELOAD_MESSAGEBOX_CANCEL_BUTTON_LABEL);
@@ skipping 218 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(ChromeJavaScriptNativeDialogCocoaFactory);
 };
 
 }  // namespace
 
 void InstallChromeJavaScriptNativeDialogFactory() {
   app_modal::JavaScriptDialogManager::GetInstance()->
       SetNativeDialogFactory(
           make_scoped_ptr(new ChromeJavaScriptNativeDialogCocoaFactory));
 }