replace NULL->nullptr in src/remoting.

remoting/host/chromeos/aura_desktop_capturer_unittest.cc

 // Copyright 2014 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 "remoting/host/chromeos/aura_desktop_capturer.h"
 
 #include "cc/output/copy_output_result.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ skipping 46 matching lines @@
   }
 
   scoped_ptr<AuraDesktopCapturer> capturer_;
 };
 
 void AuraDesktopCapturerTest::SetUp() {
   capturer_.reset(new AuraDesktopCapturer());
 }
 
 TEST_F(AuraDesktopCapturerTest, ConvertSkBitmapToDesktopFrame) {
-  webrtc::DesktopFrame* captured_frame = NULL;
+  webrtc::DesktopFrame* captured_frame = nullptr;
 
   EXPECT_CALL(*this, OnCaptureCompleted(_)).Times(1).WillOnce(
       SaveArg<0>(&captured_frame));
   capturer_->Start(this);
 
   SimulateFrameCapture();
 
-  ASSERT_TRUE(captured_frame != NULL);
+  ASSERT_TRUE(captured_frame != nullptr);
   uint8_t* captured_data = captured_frame->data();
   EXPECT_EQ(
       0,
       memcmp(
           frame_data, captured_data, sizeof(frame_data)));
 
   delete captured_frame;
 }
 
 }  // namespace remoting