Add metrics for style update time before FCP.

third_party/WebKit/Source/core/timing/PerformanceTiming.cpp

Index: third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
diff --git a/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp b/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
index 86d355a3ac7c34034e2357b9d32dbb5268195a58..a368f8f5138d310070497cb84369293057f562c7 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
+++ b/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
@@ -413,6 +413,14 @@ unsigned long long PerformanceTiming::authorStyleSheetParseDurationBeforeFCP()
       timing->authorStyleSheetParseDurationBeforeFCP());
 }
 
+unsigned long long PerformanceTiming::updateStyleDurationBeforeFCP() const {
+  const CSSTiming* timing = cssTiming();
+  if (!timing)
+    return 0;
+
+  return toIntegerMilliseconds(timing->updateDurationBeforeFCP());
+}
+
 DocumentLoader* PerformanceTiming::documentLoader() const {
   if (!frame())
     return nullptr;