Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc

Index: webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc
index c7bbfb0434428a75dd6c63462b94d230e89212c4..831077ad934f7634ca7cb32ec469e9066c5fe50a 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest.cc
@@ -1126,7 +1126,7 @@ class AcmSenderBitExactnessOldApi : public ::testing::Test,
     static const int kSourceRateHz = 32000;
     send_test_.reset(new test::AcmSendTestOldApi(
         audio_source_.get(), kSourceRateHz, kTestDurationMs));
-    return send_test_.get() != NULL;
+    return send_test_.get() != nullptr;
   }
 
   // Registers a send codec in the test::AcmSendTest object. Returns true on
@@ -1204,7 +1204,7 @@ class AcmSenderBitExactnessOldApi : public ::testing::Test,
   std::unique_ptr<test::Packet> NextPacket() override {
     auto packet = send_test_->NextPacket();
     if (!packet)
-      return NULL;
+      return nullptr;
 
     VerifyPacket(packet.get());
     // TODO(henrik.lundin) Save the packet to file as well.
@@ -1789,7 +1789,7 @@ class AcmSwitchingOutputFrequencyOldApi : public ::testing::Test,
     // "manually".
     if (num_packets_++ > kTestNumPackets) {
       EXPECT_TRUE(has_toggled_);
-      return NULL;  // Test ended.
+      return nullptr;  // Test ended.
     }
 
     // Get the next packet from the source.