Add metrics for style update time before FCP.

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

Index: third_party/WebKit/Source/core/css/CSSTiming.h
diff --git a/third_party/WebKit/Source/core/css/CSSTiming.h b/third_party/WebKit/Source/core/css/CSSTiming.h
index 3e9873e4f3e31fa10a8067ef878a1df0efdd4a20..871ef62056514c653fd831ea721429bc02166c2b 100644
--- a/third_party/WebKit/Source/core/css/CSSTiming.h
+++ b/third_party/WebKit/Source/core/css/CSSTiming.h
@@ -22,13 +22,15 @@ class CSSTiming : public GarbageCollectedFinalized<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();
 
@@ -36,6 +38,7 @@ class CSSTiming : public GarbageCollectedFinalized<CSSTiming>,
   explicit CSSTiming(Document&);
 
   double m_parseTimeBeforeFCP = 0;
+  double m_updateTimeBeforeFCP = 0;
 
   Member<Document> m_document;
   Member<PaintTiming> m_paintTiming;