Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc

Index: webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc
diff --git a/webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc b/webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc
index 0aa1cf3a4c43caf8f529c5cdfbd6ed03075da9b4..24be8b15d85874fe0db6c4e46f8ef7539dd36fef 100644
--- a/webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc
+++ b/webrtc/modules/audio_processing/echo_cancellation_impl_unittest.cc
@@ -18,13 +18,13 @@ namespace webrtc {
 
 TEST(EchoCancellationInternalTest, ExtendedFilter) {
   std::unique_ptr<AudioProcessing> ap(AudioProcessing::Create());
-  EXPECT_TRUE(ap->echo_cancellation()->aec_core() == NULL);
+  EXPECT_TRUE(ap->echo_cancellation()->aec_core() == nullptr);
 
   EXPECT_EQ(ap->kNoError, ap->echo_cancellation()->Enable(true));
   EXPECT_TRUE(ap->echo_cancellation()->is_enabled());
 
   AecCore* aec_core = ap->echo_cancellation()->aec_core();
-  ASSERT_TRUE(aec_core != NULL);
+  ASSERT_TRUE(aec_core != nullptr);
   // Disabled by default.
   EXPECT_EQ(0, WebRtcAec_extended_filter_enabled(aec_core));
 
@@ -48,13 +48,13 @@ TEST(EchoCancellationInternalTest, ExtendedFilter) {
 
 TEST(EchoCancellationInternalTest, DelayAgnostic) {
   std::unique_ptr<AudioProcessing> ap(AudioProcessing::Create());
-  EXPECT_TRUE(ap->echo_cancellation()->aec_core() == NULL);
+  EXPECT_TRUE(ap->echo_cancellation()->aec_core() == nullptr);
 
   EXPECT_EQ(ap->kNoError, ap->echo_cancellation()->Enable(true));
   EXPECT_TRUE(ap->echo_cancellation()->is_enabled());
 
   AecCore* aec_core = ap->echo_cancellation()->aec_core();
-  ASSERT_TRUE(aec_core != NULL);
+  ASSERT_TRUE(aec_core != nullptr);
   // Enabled by default.
   EXPECT_EQ(0, WebRtcAec_delay_agnostic_enabled(aec_core));