Add ServiceWorker.NavigationPreload.HeaderSize UMA

content/browser/service_worker/service_worker_metrics.h

Index: content/browser/service_worker/service_worker_metrics.h
diff --git a/content/browser/service_worker/service_worker_metrics.h b/content/browser/service_worker/service_worker_metrics.h
index 1225c38644a40fb36069a5cd64ee24583a7d63c0..9b75bd3fbec969d4d01d7107f7e499cfdadd711f 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -286,6 +286,10 @@ class ServiceWorkerMetrics {
   static void RecordStartStatusAfterFailure(int failure_count,
                                             ServiceWorkerStatusCode status);
 
+  // Records the size of Service-Worker-Navigation-Preload header when the
+  // navigation preload request is to be sent.
+  static void RecordNavigationPreloadRequestHeaderSize(size_t size);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ServiceWorkerMetrics);
 };