Add NavigationToFirstContentfulPaint UMA for ServiceWorker controlled pages.

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 4f7cb4cef832f1633c4947178db8c29021ee4c0a..52cdfc374175c57aa09abf71bfdf24fa47cfe028 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
+++ b/third_party/WebKit/Source/core/timing/PerformanceTiming.cpp
@@ -96,6 +96,15 @@ unsigned long long PerformanceTiming::unloadEventEnd() const
     return monotonicTimeToIntegerMilliseconds(timing->unloadEventEnd());
 }
 
+unsigned long long PerformanceTiming::workerStart() const
+{
+    ResourceLoadTiming* timing = resourceLoadTiming();
+    if (!timing)
+        return 0;
+
+    return monotonicTimeToIntegerMilliseconds(timing->workerStart());
+}
+
 unsigned long long PerformanceTiming::redirectStart() const
 {
     DocumentLoadTiming* timing = documentLoadTiming();