Adding instrumentation to locate the source of jankiness.

net/http/http_stream_parser.cc

Index: net/http/http_stream_parser.cc
diff --git a/net/http/http_stream_parser.cc b/net/http/http_stream_parser.cc
index 86b188b6a1f9c09fb62bb3f20f2e40461ac2e7db..4a60a6bd40e949f9ea67c52fcef2affc8fbb1590 100644
--- a/net/http/http_stream_parser.cc
+++ b/net/http/http_stream_parser.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
+#include "base/profiler/scoped_profile.h"
 #include "base/strings/string_util.h"
 #include "base/values.h"
 #include "net/base/io_buffer.h"
@@ -357,6 +358,11 @@ int HttpStreamParser::ReadResponseBody(IOBuffer* buf, int buf_len,
 }
 
 void HttpStreamParser::OnIOComplete(int result) {
+  // TODO(vadimt): Remove ScopedProfile below once crbug.com/418183 is fixed.
+  tracked_objects::ScopedProfile tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "418183 DidCompleteReadWrite => HttpStreamParser::OnIOComplete"));
+
   result = DoLoop(result);
 
   // The client callback can do anything, including destroying this class,