Adding instrumentation to locate the source of jankiness.

chrome/browser/chromeos/drive/local_file_reader.cc

Index: chrome/browser/chromeos/drive/local_file_reader.cc
diff --git a/chrome/browser/chromeos/drive/local_file_reader.cc b/chrome/browser/chromeos/drive/local_file_reader.cc
index b1ff64d73b99273f95e2d435d812202fb860f910..c29820b3e5a1dfc7c08a322c7164f845438de7c0 100644
--- a/chrome/browser/chromeos/drive/local_file_reader.cc
+++ b/chrome/browser/chromeos/drive/local_file_reader.cc
@@ -6,6 +6,7 @@
 
 #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"
@@ -49,6 +50,10 @@ void LocalFileReader::Read(net::IOBuffer* in_buffer,
 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);