Adding instrumentation to locate the source of jankiness.

net/url_request/url_request_file_job.cc

 // Copyright (c) 2012 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.
 
 // For loading files, we make use of overlapped i/o to ensure that reading from
 // the filesystem (e.g., a network filesystem) does not block the calling
 // thread.  An alternative approach would be to use a background thread or pool
 // of threads, but it seems better to leverage the operating system's ability
 // to do background file reads for us.
 //
 // Since overlapped reads require a 'static' buffer for the duration of the
 // asynchronous read, the URLRequestFileJob keeps a buffer as a member var.  In
 // URLRequestFileJob::Read, data is simply copied from the object's buffer into
 // the given buffer.  If there is no data to copy, the URLRequestFileJob
 // attempts to read more from the file to fill its buffer.  If reading from the
 // file does not complete synchronously, then the URLRequestFileJob waits for a
 // signal from the OS that the overlapped read has completed.  It does so by
 // leveraging the MessageLoop::WatchObject API.
 
 #include "net/url_request/url_request_file_job.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_util.h"
 #include "base/message_loop/message_loop.h"
+#include "base/profiler/scoped_profile.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/lock.h"
 #include "base/task_runner.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "net/base/file_stream.h"
 #include "net/base/filename_util.h"
 #include "net/base/io_buffer.h"
 #include "net/base/load_flags.h"
 #include "net/base/mime_util.h"
@@ skipping 206 matching lines @@
               base::File::FLAG_READ |
               base::File::FLAG_ASYNC;
   int rv = stream_->Open(file_path_, flags,
                          base::Bind(&URLRequestFileJob::DidOpen,
                                     weak_ptr_factory_.GetWeakPtr()));
   if (rv != ERR_IO_PENDING)
     DidOpen(rv);
 }
 
 void URLRequestFileJob::DidOpen(int result) {
+  // TODO(vadimt): Remove ScopedProfile below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedProfile tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION("423948 URLRequestFileJob::DidOpen"));
+
   if (result != OK) {
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, result));
     return;
   }
 
   if (!byte_range_.ComputeBounds(meta_info_.file_size)) {
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED,
                ERR_REQUEST_RANGE_NOT_SATISFIABLE));
     return;
   }
@@ skipping 45 matching lines @@
   if (result == 0) {
     NotifyDone(URLRequestStatus());
   } else if (result < 0) {
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, result));
   }
 
   NotifyReadComplete(result);
 }
 
 }  // namespace net