Oilpan: fix build after r200730.

Source/core/dom/DocumentTiming.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/dom/DocumentTiming.h"
 
 #include "core/dom/Document.h"
 #include "core/loader/DocumentLoader.h"
 #include "platform/TraceEvent.h"
 
 namespace blink {
 
 DocumentTiming::DocumentTiming(WeakPtrWillBeRawPtr<Document> document)
     : m_domLoading(0.0)
     , m_domInteractive(0.0)
     , m_domContentLoadedEventStart(0.0)
     , m_domContentLoadedEventEnd(0.0)
     , m_domComplete(0.0)
     , m_firstLayout(0.0)
     , m_document(document)
 {
 }
 
+DEFINE_TRACE(DocumentTiming)
+{
+    visitor->trace(m_document);
+}
+
 void DocumentTiming::notifyDocumentTimingChanged()
 {
     if (m_document && m_document->loader())
         m_document->loader()->didChangePerformanceTiming();
 }
 
 void DocumentTiming::markDomLoading()
 {
     m_domLoading = monotonicallyIncreasingTime();
     TRACE_EVENT_MARK_WITH_TIMESTAMP("blink.user_timing", "domLoading", m_domLoading);
@@ skipping 29 matching lines @@
 }
 
 void DocumentTiming::markFirstLayout()
 {
     m_firstLayout = monotonicallyIncreasingTime();
     TRACE_EVENT_MARK_WITH_TIMESTAMP("blink.user_timing", "firstLayout", m_firstLayout);
     notifyDocumentTimingChanged();
 }
 
 } // namespace blink