Adding instrumentation to locate the source of jankiness.

content/browser/service_worker/service_worker_write_to_cache_job.cc

Index: content/browser/service_worker/service_worker_write_to_cache_job.cc
diff --git a/content/browser/service_worker/service_worker_write_to_cache_job.cc b/content/browser/service_worker/service_worker_write_to_cache_job.cc
index 0baf702a25964aa3568d1e5c94261bb02f2abc2e..5e9807ba54a71d4839898b02f33bc88c246c5d1b 100644
--- a/content/browser/service_worker/service_worker_write_to_cache_job.cc
+++ b/content/browser/service_worker/service_worker_write_to_cache_job.cc
@@ -5,6 +5,7 @@
 #include "content/browser/service_worker/service_worker_write_to_cache_job.h"
 
 #include "base/debug/trace_event.h"
+#include "base/profiler/scoped_tracker.h"
 #include "content/browser/service_worker/service_worker_context_core.h"
 #include "content/browser/service_worker/service_worker_disk_cache.h"
 #include "content/browser/service_worker/service_worker_metrics.h"
@@ -332,6 +333,11 @@ void ServiceWorkerWriteToCacheJob::OnBeforeNetworkStart(
 
 void ServiceWorkerWriteToCacheJob::OnResponseStarted(
     net::URLRequest* request) {
+  // TODO(vadimt): Remove ScopedTracker below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "423948 ServiceWorkerWriteToCacheJob::OnResponseStarted"));
+
   DCHECK_EQ(net_request_, request);
   if (!request->status().is_success()) {
     AsyncNotifyDoneHelper(request->status());
@@ -373,6 +379,11 @@ void ServiceWorkerWriteToCacheJob::OnResponseStarted(
 void ServiceWorkerWriteToCacheJob::OnReadCompleted(
     net::URLRequest* request,
     int bytes_read) {
+  // TODO(vadimt): Remove ScopedTracker below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "423948 ServiceWorkerWriteToCacheJob::OnReadCompleted"));
+
   DCHECK_EQ(net_request_, request);
   if (bytes_read < 0) {
     DCHECK(!request->status().is_success());