Adding instrumentation to locate the source of jankiness.

chrome/browser/chromeos/drive/local_file_reader.cc

 // Copyright 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 "chrome/browser/chromeos/drive/local_file_reader.h"
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
+#include "base/profiler/scoped_profile.h"
 #include "base/sequenced_task_runner.h"
 #include "net/base/completion_callback.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 
 namespace drive {
 namespace util {
 
 LocalFileReader::LocalFileReader(
     base::SequencedTaskRunner* sequenced_task_runner)
@@ skipping 23 matching lines @@
                            const net::CompletionCallback& callback) {
   DCHECK(!callback.is_null());
   DCHECK(file_stream_.IsOpen());
   int rv = file_stream_.Read(in_buffer, buffer_length, callback);
   DCHECK_EQ(rv, net::ERR_IO_PENDING);
 }
 
 void LocalFileReader::DidOpen(const net::CompletionCallback& callback,
                               int64 offset,
                               int error) {
+  // TODO(vadimt): Remove ScopedProfile below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedProfile tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION("423948 LocalFileReader::DidOpen"));
+
   if (error != net::OK)
     return callback.Run(error);
 
   int rv = file_stream_.Seek(base::File::FROM_BEGIN, offset,
                              Bind(&LocalFileReader::DidSeek,
                                   weak_ptr_factory_.GetWeakPtr(),
                                   callback, offset));
   DCHECK_EQ(rv, net::ERR_IO_PENDING);
 }
 
 void LocalFileReader::DidSeek(const net::CompletionCallback& callback,
                               int64 offset,
                               int64 error) {
   callback.Run(error == offset ? net::OK : net::ERR_FAILED);
 }
 
 }  // namespace util
 }  // namespace drive