Use a new Supplement constructor for Supplement<Document> (Part 1)

third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp

Index: third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp
diff --git a/third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp b/third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp
index 055942495eb99590259217730943669568a99812..3abaf1dba7458ecd030ab3593c1179e7f287b005 100644
--- a/third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp
+++ b/third_party/WebKit/Source/core/dom/DocumentParserTiming.cpp
@@ -65,16 +65,15 @@ void DocumentParserTiming::recordParserBlockedOnScriptExecutionDuration(
 }
 
 DEFINE_TRACE(DocumentParserTiming) {
-  visitor->trace(m_document);
   Supplement<Document>::trace(visitor);
 }
 
 DocumentParserTiming::DocumentParserTiming(Document& document)
-    : m_document(document) {}
+    : Supplement<Document>(document) {}
 
 void DocumentParserTiming::notifyDocumentParserTimingChanged() {
-  if (m_document->loader())
-    m_document->loader()->didChangePerformanceTiming();
+  if (host()->loader())
+    host()->loader()->didChangePerformanceTiming();
 }
 
 }  // namespace blink