Adding instrumentation to locate the source of jankiness.

storage/browser/fileapi/file_writer_delegate.cc

Index: storage/browser/fileapi/file_writer_delegate.cc
diff --git a/storage/browser/fileapi/file_writer_delegate.cc b/storage/browser/fileapi/file_writer_delegate.cc
index fc533eb006cb40f3b34ff55f8256b84ebd4f518c..1b942c438ebc8f3e95aeaaaad907e862af4db7ab 100644
--- a/storage/browser/fileapi/file_writer_delegate.cc
+++ b/storage/browser/fileapi/file_writer_delegate.cc
@@ -9,6 +9,7 @@
 #include "base/files/file_util_proxy.h"
 #include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/sequenced_task_runner.h"
 #include "base/threading/thread_restrictions.h"
 #include "net/base/net_errors.h"
@@ -90,6 +91,11 @@ void FileWriterDelegate::OnSSLCertificateError(net::URLRequest* request,
 }
 
 void FileWriterDelegate::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 FileWriterDelegate::OnResponseStarted"));
+
   DCHECK_EQ(request_.get(), request);
   if (!request->status().is_success() || request->GetResponseCode() != 200) {
     OnError(base::File::FILE_ERROR_FAILED);
@@ -100,6 +106,11 @@ void FileWriterDelegate::OnResponseStarted(net::URLRequest* request) {
 
 void FileWriterDelegate::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 FileWriterDelegate::OnReadCompleted"));
+
   DCHECK_EQ(request_.get(), request);
   if (!request->status().is_success()) {
     OnError(base::File::FILE_ERROR_FAILED);