cc: Change scoped_ptr<T>() to nullptr.

cc/test/layer_tree_pixel_test.cc

 // 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 "cc/test/layer_tree_pixel_test.h"
 
 #include "base/command_line.h"
 #include "base/path_service.h"
 #include "cc/base/switches.h"
 #include "cc/layers/solid_color_layer.h"
@@ skipping 112 matching lines @@
   layer->SetBounds(rect.size());
   layer->SetPosition(rect.origin());
   layer->SetBackgroundColor(color);
   return layer;
 }
 
 void LayerTreePixelTest::EndTest() {
   // Drop TextureMailboxes on the main thread so that they can be cleaned up and
   // the pending callbacks will fire.
   for (size_t i = 0; i < texture_layers_.size(); ++i) {
-    texture_layers_[i]->SetTextureMailbox(TextureMailbox(),
-                                          scoped_ptr<SingleReleaseCallback>());
+    texture_layers_[i]->SetTextureMailbox(TextureMailbox(), nullptr);
   }
 
   TryEndTest();
 }
 
 void LayerTreePixelTest::TryEndTest() {
   if (!result_bitmap_)
     return;
   if (pending_texture_mailbox_callbacks_)
     return;
@@ skipping 216 matching lines @@
 
   *texture_mailbox = TextureMailbox(mailbox, GL_TEXTURE_2D, sync_point);
   *release_callback = SingleReleaseCallback::Create(
       base::Bind(&LayerTreePixelTest::ReleaseTextureMailbox,
                  base::Unretained(this),
                  base::Passed(&context),
                  texture_id));
 }
 
 }  // namespace cc