Add a JavaScript dialog tab helper.

chrome/browser/extensions/content_script_apitest.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 <stddef.h>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
@@ skipping 146 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(DialogClient);
 };
 
 DialogHelper::DialogHelper(content::WebContents* web_contents)
     : dialog_count_(0),
       web_contents_(web_contents),
       dialog_manager_(nullptr),
       client_(nullptr) {
   app_modal::JavaScriptDialogManager* dialog_manager_impl =
       app_modal::JavaScriptDialogManager::GetInstance();
+  client_ = new DialogClient(this);
+  dialog_manager_impl->SetExtensionsClient(base::WrapUnique(client_));
+
   dialog_manager_ =
       web_contents_->GetDelegate()->GetJavaScriptDialogManager(web_contents_);
-  DCHECK_EQ(dialog_manager_impl, dialog_manager_);
-
-  client_ = new DialogClient(this);
-  dialog_manager_impl->SetExtensionsClient(base::WrapUnique(client_));
 }
 
 DialogHelper::~DialogHelper() {
   client_->set_helper(nullptr);
 }
 
 void DialogHelper::CloseDialogs() {
   dialog_manager_->CancelActiveAndPendingDialogs(web_contents_);
 }
 
@@ skipping 441 matching lines @@
   ExtensionTestMessageListener iframe_loaded_listener("iframe loaded", false);
   ExtensionTestMessageListener content_script_listener("script injected",
                                                        false);
   LoadExtension(data_dir.AppendASCII("script_a_com"));
   LoadExtension(data_dir.AppendASCII("background_page_iframe"));
   iframe_loaded_listener.WaitUntilSatisfied();
   EXPECT_FALSE(content_script_listener.was_satisfied());
 }
 
 }  // namespace extensions