Adding instrumentation to locate the source of jankiness.

storage/browser/fileapi/local_file_stream_writer.cc

Index: storage/browser/fileapi/local_file_stream_writer.cc
diff --git a/storage/browser/fileapi/local_file_stream_writer.cc b/storage/browser/fileapi/local_file_stream_writer.cc
index 0eb555f9262127cef9c617dba3210797e0020c61..968b5fe979ae89b1ff5874902427b392239791aa 100644
--- a/storage/browser/fileapi/local_file_stream_writer.cc
+++ b/storage/browser/fileapi/local_file_stream_writer.cc
@@ -6,6 +6,7 @@
 
 #include "base/callback.h"
 #include "base/message_loop/message_loop.h"
+#include "base/profiler/scoped_profile.h"
 #include "net/base/file_stream.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
@@ -125,6 +126,11 @@ void LocalFileStreamWriter::DidOpen(
     const net::CompletionCallback& error_callback,
     const base::Closure& main_operation,
     int result) {
+  // TODO(vadimt): Remove ScopedProfile below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedProfile tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "423948 LocalFileStreamWriter::DidOpen"));
+
   DCHECK(has_pending_operation_);
   DCHECK(stream_impl_.get());