Adding instrumentation to locate the source of jankiness.

net/url_request/url_fetcher_response_writer.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/url_request/url_fetcher_response_writer.h"
 
 #include "base/files/file_util.h"
 #include "base/location.h"
+#include "base/profiler/scoped_profile.h"
 #include "base/sequenced_task_runner.h"
 #include "base/task_runner_util.h"
 #include "net/base/file_stream.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 
 namespace net {
 
 URLFetcherStringWriter* URLFetcherResponseWriter::AsStringWriter() {
   return NULL;
@@ skipping 147 matching lines @@
       base::File::FLAG_OPEN,
       base::Bind(&URLFetcherFileWriter::DidOpenFile,
                  weak_factory_.GetWeakPtr(),
                  callback));
   if (result != ERR_IO_PENDING)
     DidOpenFile(callback, result);
 }
 
 void URLFetcherFileWriter::DidOpenFile(const CompletionCallback& callback,
                                        int result) {
+  // TODO(vadimt): Remove ScopedProfile below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedProfile tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "423948 URLFetcherFileWriter::DidOpenFile"));
+
   if (result == OK)
     owns_file_ = true;
   else
     CloseAndDeleteFile();
 
   callback.Run(result);
 }
 
 void URLFetcherFileWriter::CloseComplete(const CompletionCallback& callback,
                                          int result) {
   // Destroy |file_stream_| whether or not the close succeeded.
   file_stream_.reset();
   callback.Run(result);
 }
 
 }  // namespace net