Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/editing/FrameSelection.cpp

Index: Source/core/editing/FrameSelection.cpp
diff --git a/Source/core/editing/FrameSelection.cpp b/Source/core/editing/FrameSelection.cpp
index 7f546b843f7d30e590e60620649c4d9b984d2f82..0d70bd092225b463e072fa938bcd23d94fb1f8cd 100644
--- a/Source/core/editing/FrameSelection.cpp
+++ b/Source/core/editing/FrameSelection.cpp
@@ -1357,7 +1357,7 @@ void FrameSelection::selectAll()
         }
     }
 
-    RefPtr<Node> root = 0;
+    RefPtr<Node> root = nullptr;
     Node* selectStartTarget = 0;
     if (isContentEditable()) {
         root = highestEditableRoot(m_selection.start());
@@ -1654,7 +1654,7 @@ void FrameSelection::setFocusedNodeIfNeeded()
             }
             target = target->parentOrShadowHostElement();
         }
-        m_frame->document()->setFocusedElement(0);
+        m_frame->document()->setFocusedElement(nullptr);
     }
 
     if (caretBrowsing)