Replace NULL with nullptr in all C++ files.

webrtc/common_video/libyuv/libyuv_unittest.cc

Index: webrtc/common_video/libyuv/libyuv_unittest.cc
diff --git a/webrtc/common_video/libyuv/libyuv_unittest.cc b/webrtc/common_video/libyuv/libyuv_unittest.cc
index 8f421f3038d17c0f8ebad2ebc23ae241a58eaff6..c528dfb027cd7b7262316fd4e1a9e7e626655821 100644
--- a/webrtc/common_video/libyuv/libyuv_unittest.cc
+++ b/webrtc/common_video/libyuv/libyuv_unittest.cc
@@ -47,7 +47,7 @@ class TestLibYuv : public ::testing::Test {
 };
 
 TestLibYuv::TestLibYuv()
-    : source_file_(NULL),
+    : source_file_(nullptr),
       orig_frame_(),
       width_(352),
       height_(288),
@@ -59,8 +59,8 @@ void TestLibYuv::SetUp() {
   const std::string input_file_name = webrtc::test::ResourcePath("foreman_cif",
                                                                  "yuv");
   source_file_  = fopen(input_file_name.c_str(), "rb");
-  ASSERT_TRUE(source_file_ != NULL) << "Cannot read file: "<<
-                                       input_file_name << "\n";
+  ASSERT_TRUE(source_file_ != nullptr)
+      << "Cannot read file: " << input_file_name << "\n";
 
   rtc::scoped_refptr<VideoFrameBuffer> buffer(
       test::ReadI420Buffer(width_, height_, source_file_));
@@ -69,10 +69,10 @@ void TestLibYuv::SetUp() {
 }
 
 void TestLibYuv::TearDown() {
-  if (source_file_ != NULL) {
+  if (source_file_ != nullptr) {
     ASSERT_EQ(0, fclose(source_file_));
   }
-  source_file_ = NULL;
+  source_file_ = nullptr;
 }
 
 TEST_F(TestLibYuv, ConvertSanityTest) {
@@ -85,7 +85,7 @@ TEST_F(TestLibYuv, ConvertTest) {
   std::string output_file_name = webrtc::test::OutputPath() +
                                  "LibYuvTest_conversion.yuv";
   FILE*  output_file = fopen(output_file_name.c_str(), "wb");
-  ASSERT_TRUE(output_file != NULL);
+  ASSERT_TRUE(output_file != nullptr);
 
   double psnr = 0.0;
 
@@ -204,7 +204,7 @@ TEST_F(TestLibYuv, ConvertAlignedFrame) {
   std::string output_file_name = webrtc::test::OutputPath() +
                                  "LibYuvTest_conversion.yuv";
   FILE*  output_file = fopen(output_file_name.c_str(), "wb");
-  ASSERT_TRUE(output_file != NULL);
+  ASSERT_TRUE(output_file != nullptr);
 
   double psnr = 0.0;