Add metrics for style update time before FCP.

third_party/WebKit/Source/core/css/CSSTiming.h

 // Copyright 2016 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.
 
 #ifndef CSSTiming_h
 #define CSSTiming_h
 
 #include "core/dom/Document.h"
 #include "platform/Supplementable.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
 class PaintTiming;
 
 class CSSTiming : public GarbageCollectedFinalized<CSSTiming>,
                   public Supplement<Document> {
   WTF_MAKE_NONCOPYABLE(CSSTiming);
   USING_GARBAGE_COLLECTED_MIXIN(CSSTiming);
 
  public:
   virtual ~CSSTiming() {}
 
-  // TODO(csharrison): Also record update style time before first paint.
   void recordAuthorStyleSheetParseTime(double seconds);
+  void recordUpdateDuration(double seconds);
 
   double authorStyleSheetParseDurationBeforeFCP() const {
     return m_parseTimeBeforeFCP;
   }
 
+  double updateDurationBeforeFCP() const { return m_updateTimeBeforeFCP; }
+
   static CSSTiming& from(Document&);
   DECLARE_VIRTUAL_TRACE();
 
  private:
   explicit CSSTiming(Document&);
 
   double m_parseTimeBeforeFCP = 0;
+  double m_updateTimeBeforeFCP = 0;
 
   Member<Document> m_document;
   Member<PaintTiming> m_paintTiming;
 };
 
 }  // namespace blink
 
 #endif  // CSSTiming_h