Add ServiceWorker.NavigationPreload.HeaderSize UMA

content/browser/service_worker/service_worker_fetch_dispatcher.cc

Index: content/browser/service_worker/service_worker_fetch_dispatcher.cc
diff --git a/content/browser/service_worker/service_worker_fetch_dispatcher.cc b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
index 6e5bb228d921dcff58660819c9186c7c9f63a2c8..b7bcb49f5f4a96ebc894b1fab427fe250a475d35 100644
--- a/content/browser/service_worker/service_worker_fetch_dispatcher.cc
+++ b/content/browser/service_worker/service_worker_fetch_dispatcher.cc
@@ -17,6 +17,7 @@
 #include "content/browser/loader/resource_requester_info.h"
 #include "content/browser/loader/url_loader_factory_impl.h"
 #include "content/browser/service_worker/embedded_worker_status.h"
+#include "content/browser/service_worker/service_worker_metrics.h"
 #include "content/browser/service_worker/service_worker_version.h"
 #include "content/common/service_worker/service_worker_event_dispatcher.mojom.h"
 #include "content/common/service_worker/service_worker_messages.h"
@@ -446,6 +447,8 @@ void ServiceWorkerFetchDispatcher::MaybeStartNavigationPreload(
   request.is_main_frame = original_info->IsMainFrame();
   request.parent_is_main_frame = original_info->ParentIsMainFrame();
 
+  ServiceWorkerMetrics::RecordNavigationPreloadRequestHeaderSize(
+      version_->navigation_preload_state().header.length());

[falken, 2017/01/11 05:28:05]

nit: seems better to put this below line 452 or even line 455.

[horo, 2017/01/11 06:13:07]

Done.

   DCHECK(net::HttpUtil::IsValidHeaderValue(
       version_->navigation_preload_state().header));
   request.headers = "Service-Worker-Navigation-Preload: " +