Rewrite scoped_ptr<T>(NULL) to use the default ctor.

ui/app_list/cocoa/app_list_view_controller_unittest.mm

 // Copyright 2013 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 "base/mac/scoped_nsobject.h"
 #import "testing/gtest_mac.h"
 #import "ui/app_list/cocoa/app_list_view_controller.h"
 #import "ui/app_list/cocoa/apps_grid_controller.h"
 #import "ui/app_list/cocoa/test/apps_grid_controller_test_helper.h"
 #include "ui/app_list/test/app_list_test_model.h"
 #include "ui/app_list/test/app_list_test_view_delegate.h"
 
 namespace app_list {
 namespace test {
 
 class AppListViewControllerTest : public AppsGridControllerTestHelper {
  public:
   AppListViewControllerTest() {}
 
   virtual void SetUp() OVERRIDE {
     app_list_view_controller_.reset([[AppListViewController alloc] init]);
     SetUpWithGridController([app_list_view_controller_ appsGridController]);
     [[test_window() contentView] addSubview:[app_list_view_controller_ view]];
   }
 
   virtual void TearDown() OVERRIDE {
     [app_list_view_controller_
-        setDelegate:scoped_ptr<app_list::AppListViewDelegate>(NULL)];
+        setDelegate:scoped_ptr<app_list::AppListViewDelegate>()];
     app_list_view_controller_.reset();
     AppsGridControllerTestHelper::TearDown();
   }
 
   virtual void ResetModel(scoped_ptr<AppListModel> new_model) OVERRIDE {
     scoped_ptr<AppListViewDelegate> delegate_(new AppListTestViewDelegate);
     [app_list_view_controller_ setDelegate:delegate_.Pass()
                              withTestModel:new_model.Pass()];
   }
 
@@ skipping 44 matching lines @@
   // Replace with a single page model, and ensure we go back to the first page.
   ReplaceTestModel(1);
   EXPECT_EQ(0u, [apps_grid_controller_ visiblePage]);
   EXPECT_EQ(0, [pager selectedSegment]);
   EXPECT_EQ(1, [pager segmentCount]);
   EXPECT_EQ(1.0, [apps_grid_controller_ visiblePortionOfPage:0]);
 }
 
 }  // namespace test
 }  // namespace app_list