Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc

Index: webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc
diff --git a/webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc b/webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc
index 8299924adfa73f90ed391063d86a1c4d1eae4538..c282305c32592d489a711b751946c3f750a36bc3 100644
--- a/webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc
+++ b/webrtc/modules/audio_coding/neteq/time_stretch_unittest.cc
@@ -46,13 +46,13 @@ TEST(TimeStretch, CreateUsingFactory) {
   AccelerateFactory accelerate_factory;
   Accelerate* accelerate =
       accelerate_factory.Create(kSampleRate, kNumChannels, bgn);
-  EXPECT_TRUE(accelerate != NULL);
+  EXPECT_TRUE(accelerate != nullptr);
   delete accelerate;
 
   PreemptiveExpandFactory preemptive_expand_factory;
   PreemptiveExpand* preemptive_expand = preemptive_expand_factory.Create(
       kSampleRate, kNumChannels, bgn, kOverlapSamples);
-  EXPECT_TRUE(preemptive_expand != NULL);
+  EXPECT_TRUE(preemptive_expand != nullptr);
   delete preemptive_expand;
 }