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

webrtc/base/signalthread_unittest.cc

 /*
  *  Copyright 2004 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 18 matching lines @@
 
     virtual ~SlowSignalThread() {
       EXPECT_EQ(harness_->main_thread_, Thread::Current());
       ++harness_->thread_deleted_;
     }
 
     const SignalThreadTest* harness() { return harness_; }
 
    protected:
     virtual void OnWorkStart() {
-      ASSERT_TRUE(harness_ != NULL);
+      ASSERT_TRUE(harness_ != nullptr);
       ++harness_->thread_started_;
       EXPECT_EQ(harness_->main_thread_, Thread::Current());
       EXPECT_FALSE(worker()->RunningForTest());  // not started yet
     }
 
     virtual void OnWorkStop() {
       ++harness_->thread_stopped_;
       EXPECT_EQ(harness_->main_thread_, Thread::Current());
       EXPECT_TRUE(worker()->RunningForTest());  // not stopped yet
     }
@@ skipping 146 matching lines @@
   EXPECT_STATE(1, 0, 0, 1, 1);
 }
 
 TEST_F(SignalThreadTest, DeferredDestroyedThreadCleansUp) {
   thread_->Start();
   EXPECT_STATE(1, 0, 0, 0, 0);
   thread_->Destroy(false);
   EXPECT_STATE(1, 0, 0, 1, 0);
   EXPECT_STATE_WAIT(1, 1, 0, 1, 1, kTimeout);
 }