Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp

Index: Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp
diff --git a/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp b/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp
index b879c84ac298194ed42f86171b4ce3a5fdc81751..275925bd16920b63ab34c91b71d6dbe1b58d382c 100644
--- a/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp
+++ b/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.cpp
@@ -54,7 +54,7 @@ void PlatformSpeechSynthesizerMock::speakingFinished(Timer<PlatformSpeechSynthes
 {
     ASSERT(m_utterance.get());
     client()->didFinishSpeaking(m_utterance);
-    m_utterance = 0;
+    m_utterance = nullptr;
 }
 
 void PlatformSpeechSynthesizerMock::initializeVoiceList()
@@ -86,7 +86,7 @@ void PlatformSpeechSynthesizerMock::cancel()
 
     m_speakingFinishedTimer.stop();
     client()->speakingErrorOccurred(m_utterance);
-    m_utterance = 0;
+    m_utterance = nullptr;
 }
 
 void PlatformSpeechSynthesizerMock::pause()