Fix a crash when we try to close a js dialog that wasn't shown.

chrome/browser/js_modal_dialog.cc

 // Copyright (c) 2010 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/js_modal_dialog.h"
 
 #include "base/string_util.h"
 #include "chrome/browser/extensions/extension_host.h"
 #include "chrome/browser/tab_contents/tab_contents.h"
 #include "chrome/common/notification_service.h"
@@ skipping 11 matching lines @@
 JavaScriptAppModalDialog::JavaScriptAppModalDialog(
     JavaScriptMessageBoxClient* client,
     const std::wstring& title,
     int dialog_flags,
     const std::wstring& message_text,
     const std::wstring& default_prompt_text,
     bool display_suppress_checkbox,
     bool is_before_unload_dialog,
     IPC::Message* reply_msg)
     : AppModalDialog(client->AsTabContents(), title),
+#if defined(OS_MACOSX)
+      dialog_(NULL),
+#endif
       client_(client),
       extension_host_(client->AsExtensionHost()),
       dialog_flags_(dialog_flags),
       display_suppress_checkbox_(display_suppress_checkbox),
       is_before_unload_dialog_(is_before_unload_dialog),
       reply_msg_(reply_msg) {
   // We trim the various parts of the message dialog because otherwise we can
   // overflow the message dialog (and crash/hang the GTK+ version).
   ElideString(message_text, kMessageTextMaxSize, &message_text_);
   ElideString(default_prompt_text, kDefaultPromptTextSize,
@@ skipping 15 matching lines @@
   if (NotificationType::EXTENSION_HOST_DESTROYED == type &&
       Details<ExtensionHost>(extension_host_) != details)
     return;
 
   // If we reach here, we know the notification is relevant to us, either
   // because we're only observing applicable sources or because we passed the
   // check above. Both of those indicate that we should ignore this dialog.
   // Also clear the client, since it's now invalid.
   skip_this_dialog_ = true;
   client_ = NULL;
-  CloseModalDialog();
+  if (dialog_)
+    CloseModalDialog();
 }
 
 void JavaScriptAppModalDialog::InitNotifications() {
   // Make sure we get relevant navigation notifications so we know when our
   // parent contents will disappear or navigate to a different page.
   if (tab_contents_) {
     registrar_.Add(this, NotificationType::NAV_ENTRY_COMMITTED,
                    Source<NavigationController>(&tab_contents_->controller()));
     registrar_.Add(this, NotificationType::TAB_CONTENTS_DESTROYED,
                    Source<TabContents>(tab_contents_));
@@ skipping 51 matching lines @@
 // state, destroying the host. http://crbug.com/29355
 #if !defined(OS_MACOSX)
     else if (extension_host_)
       extension_host_->OnMessageBoxClosed(reply_msg_, false, L"");
     else
       NOTREACHED();
 #endif
   }
   AppModalDialog::Cleanup();
 }
-