Remove "top_down" flag in the message center code

ui/message_center/views/message_list_view_unittest.cc

 // Copyright 2016 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 <map>
 #include <memory>
 #include <utility>
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
@@ skipping 75 matching lines @@
                             public MessageListView::Observer,
                             public MessageCenterController {
  public:
   MessageListViewTest() {}
 
   ~MessageListViewTest() override {}
 
   void SetUp() override {
     views::ViewsTestBase::SetUp();
 
-    message_list_view_.reset(new MessageListView(false /* top_down */));
+    message_list_view_.reset(new MessageListView());
     message_list_view_->AddObserver(this);
     message_list_view_->set_owned_by_client();
 
     widget_.reset(new views::Widget());
     views::Widget::InitParams params =
         CreateParams(views::Widget::InitParams::TYPE_POPUP);
     params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
     params.bounds = gfx::Rect(50, 50, 650, 650);
     widget_->Init(params);
     views::View* root = widget_->GetRootView();
@@ skipping 69 matching lines @@
   EXPECT_FALSE(message_list_view()->Contains(notification_view));
 
   // Add a notification.
   message_list_view()->AddNotificationAt(notification_view, 0);
 
   EXPECT_EQ(1, message_list_view()->child_count());
   EXPECT_TRUE(message_list_view()->Contains(notification_view));
 }
 
 }  // namespace