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.
 //
@@ skipping 252 matching lines @@
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED,
                ERR_REQUEST_RANGE_NOT_SATISFIABLE));
     return;
   }
 
   remaining_bytes_ = byte_range_.last_byte_position() -
                      byte_range_.first_byte_position() + 1;
   DCHECK_GE(remaining_bytes_, 0);
 
   if (remaining_bytes_ > 0 && byte_range_.first_byte_position() != 0) {
+    // TODO(vadimt): Remove ScopedProfile below once crbug.com/423948 is fixed.
+    tracked_objects::ScopedProfile tracking_profile1(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "423948 URLRequestFileJob::DidOpen 1"));
+
     int rv = stream_->Seek(base::File::FROM_BEGIN,
                            byte_range_.first_byte_position(),
                            base::Bind(&URLRequestFileJob::DidSeek,
                                       weak_ptr_factory_.GetWeakPtr()));
     if (rv != ERR_IO_PENDING) {
       // stream_->Seek() failed, so pass an intentionally erroneous value
       // into DidSeek().
       DidSeek(-1);
     }
   } else {
@@ skipping 29 matching lines @@
   if (result == 0) {
     NotifyDone(URLRequestStatus());
   } else if (result < 0) {
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, result));
   }
 
   NotifyReadComplete(result);
 }
 
 }  // namespace net