Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/test/auto_test/standard/mixing_test.cc

Index: webrtc/voice_engine/test/auto_test/standard/mixing_test.cc
diff --git a/webrtc/voice_engine/test/auto_test/standard/mixing_test.cc b/webrtc/voice_engine/test/auto_test/standard/mixing_test.cc
index 8a1807209a8695baf18688a153ce878fb94c0d10..104d118dcb192bbd017357e0d62bb7af16980461 100644
--- a/webrtc/voice_engine/test/auto_test/standard/mixing_test.cc
+++ b/webrtc/voice_engine/test/auto_test/standard/mixing_test.cc
@@ -111,7 +111,7 @@ class MixingTest : public AfterInitializationFixture {
   // will be twice the duration of the test.
   void GenerateInputFile(int16_t input_value) {
     FILE* input_file = fopen(input_filename_.c_str(), "wb");
-    ASSERT_TRUE(input_file != NULL);
+    ASSERT_TRUE(input_file != nullptr);
     for (int i = 0; i < kInSampleRateHz / 1000 * (kTestDurationMs * 2); i++) {
       ASSERT_EQ(1u, fwrite(&input_value, sizeof(input_value), 1, input_file));
     }
@@ -121,7 +121,7 @@ class MixingTest : public AfterInitializationFixture {
   void VerifyMixedOutput(int16_t max_output_value, int16_t min_output_value) {
     // Verify the mixed output.
     FILE* output_file = fopen(output_filename_.c_str(), "rb");
-    ASSERT_TRUE(output_file != NULL);
+    ASSERT_TRUE(output_file != nullptr);
     int16_t output_value = 0;
     int samples_read = 0;
     while (fread(&output_value, sizeof(output_value), 1, output_file) == 1) {
@@ -203,7 +203,7 @@ class MixingTest : public AfterInitializationFixture {
 
   int GetFileDurationMs(const char* file_name) {
     FILE* fid = fopen(file_name, "rb");
-    EXPECT_FALSE(fid == NULL);
+    EXPECT_FALSE(fid == nullptr);
     fseek(fid, 0, SEEK_END);
     int size = ftell(fid);
     EXPECT_NE(-1, size);