Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp

Index: Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp
diff --git a/Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp b/Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp
index c8f143086d2ff9fb731709f9c7f1fbba514aeca9..5044875f6c66488a8c788ff1c5ef38ba0def9cea 100644
--- a/Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp
+++ b/Source/platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.cpp
@@ -116,7 +116,7 @@ FontPlatformData::FontPlatformData(const FontPlatformData& src)
     , m_syntheticItalic(src.m_syntheticItalic)
     , m_orientation(src.m_orientation)
     , m_style(src.m_style)
-    , m_harfBuzzFace(0)
+    , m_harfBuzzFace(nullptr)
     , m_isHashTableDeletedValue(false)
 {
 }
@@ -142,7 +142,7 @@ FontPlatformData::FontPlatformData(const FontPlatformData& src, float textSize)
     , m_syntheticBold(src.m_syntheticBold)
     , m_syntheticItalic(src.m_syntheticItalic)
     , m_orientation(src.m_orientation)
-    , m_harfBuzzFace(0)
+    , m_harfBuzzFace(nullptr)
     , m_isHashTableDeletedValue(false)
 {
     querySystemForRenderStyle(FontDescription::subpixelPositioning());
@@ -168,7 +168,7 @@ FontPlatformData& FontPlatformData::operator=(const FontPlatformData& src)
     m_textSize = src.m_textSize;
     m_syntheticBold = src.m_syntheticBold;
     m_syntheticItalic = src.m_syntheticItalic;
-    m_harfBuzzFace = 0;
+    m_harfBuzzFace = nullptr;
     m_orientation = src.m_orientation;
     m_style = src.m_style;
     m_emSizeInFontUnits = src.m_emSizeInFontUnits;