Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/test/TwoWayCommunication.cc

Index: webrtc/modules/audio_coding/test/TwoWayCommunication.cc
diff --git a/webrtc/modules/audio_coding/test/TwoWayCommunication.cc b/webrtc/modules/audio_coding/test/TwoWayCommunication.cc
index f575b2a0a42c5827627b767949d4b0193c01ff32..122d966fb82135cc7514c06e3bb0b5784f7a536d 100644
--- a/webrtc/modules/audio_coding/test/TwoWayCommunication.cc
+++ b/webrtc/modules/audio_coding/test/TwoWayCommunication.cc
@@ -74,11 +74,11 @@ void TwoWayCommunication::ChooseCodec(uint8_t* codecID_A,
   }
   printf("\nChoose a send codec for side A [0]: ");
   char myStr[15] = "";
-  EXPECT_TRUE(fgets(myStr, 10, stdin) != NULL);
+  EXPECT_TRUE(fgets(myStr, 10, stdin) != nullptr);
   *codecID_A = (uint8_t) atoi(myStr);
 
   printf("\nChoose a send codec for side B [0]: ");
-  EXPECT_TRUE(fgets(myStr, 10, stdin) != NULL);
+  EXPECT_TRUE(fgets(myStr, 10, stdin) != nullptr);
   *codecID_B = (uint8_t) atoi(myStr);
 
   printf("\n");