Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/transient/wpd_node_unittest.cc

Index: webrtc/modules/audio_processing/transient/wpd_node_unittest.cc
diff --git a/webrtc/modules/audio_processing/transient/wpd_node_unittest.cc b/webrtc/modules/audio_processing/transient/wpd_node_unittest.cc
index 3a9cb759f210078d05dcf99ad45e50d3ad2f7de7..e6047945da7e0e25dd30c8446766b3ee78aaf45c 100644
--- a/webrtc/modules/audio_processing/transient/wpd_node_unittest.cc
+++ b/webrtc/modules/audio_processing/transient/wpd_node_unittest.cc
@@ -57,9 +57,9 @@ TEST(WPDNodeTest, UpdateWithArbitraryDataAndArbitraryFilter) {
 TEST(WPDNodeTest, ExpectedErrorReturnValue) {
   WPDNode node(kDataLength, kCoefficients, kCoefficientsLength);
   EXPECT_EQ(-1, node.Update(kParentData, kParentDataLength - 1));
-  EXPECT_EQ(-1, node.Update(NULL, kParentDataLength));
+  EXPECT_EQ(-1, node.Update(nullptr, kParentDataLength));
   EXPECT_EQ(-1, node.set_data(kParentData, kDataLength - 1));
-  EXPECT_EQ(-1, node.set_data(NULL, kDataLength));
+  EXPECT_EQ(-1, node.set_data(nullptr, kDataLength));
 }
 
 }  // namespace webrtc