Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/HTMLTableRowElement.cpp

Index: Source/core/html/HTMLTableRowElement.cpp
diff --git a/Source/core/html/HTMLTableRowElement.cpp b/Source/core/html/HTMLTableRowElement.cpp
index 1452c0e19a44e87a00eb0f08059f2c6862f7111f..802e96bc94d905490c77a3abbe2d5e4b12bd4375 100644
--- a/Source/core/html/HTMLTableRowElement.cpp
+++ b/Source/core/html/HTMLTableRowElement.cpp
@@ -119,7 +119,7 @@ PassRefPtr<HTMLElement> HTMLTableRowElement::insertCell(int index, ExceptionStat
     int numCells = children ? children->length() : 0;
     if (index < -1 || index > numCells) {
         exceptionState.throwDOMException(IndexSizeError, "The value provided (" + String::number(index) + ") is outside the range [-1, " + String::number(numCells) + "].");
-        return 0;
+        return nullptr;
     }
 
     RefPtr<HTMLTableCellElement> cell = HTMLTableCellElement::create(tdTag, document());