Replace NULL with nullptr or null in webrtc/base/.

webrtc/base/event_tracer_unittest.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 14 matching lines @@
     events_logged_ = 0;
   }
 
   void Increment() {
     ++events_logged_;
   }
 
   int Count() const { return events_logged_; }
 
   static TestStatistics* Get() {
-    static TestStatistics* test_stats = NULL;
+    static TestStatistics* test_stats = nullptr;
     if (!test_stats)
       test_stats = new TestStatistics();
     return test_stats;
   }
 
  private:
   int events_logged_;
 };
 
 static const unsigned char* GetCategoryEnabledHandler(const char* name) {
@@ skipping 27 matching lines @@
 TEST(EventTracerTest, ScopedTraceEvent) {
   SetupEventTracer(&GetCategoryEnabledHandler, &AddTraceEventHandler);
   {
     TRACE_EVENT0("test", "ScopedTraceEvent");
   }
   EXPECT_EQ(2, TestStatistics::Get()->Count());
   TestStatistics::Get()->Reset();
 }
 
 }  // namespace webrtc