Adding instrumentation to locate the source of jankiness.

chrome/browser/net/connection_tester.cc

Index: chrome/browser/net/connection_tester.cc
diff --git a/chrome/browser/net/connection_tester.cc b/chrome/browser/net/connection_tester.cc
index ae905e02f5f8668a5461e1c9e15156720072981f..fcac4902a32ee49246e1b7dccb77f9f46e95b914 100644
--- a/chrome/browser/net/connection_tester.cc
+++ b/chrome/browser/net/connection_tester.cc
@@ -10,6 +10,7 @@
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/thread_restrictions.h"
@@ -343,6 +344,11 @@ class ConnectionTester::TestRunner : public net::URLRequest::Delegate {
 };
 
 void ConnectionTester::TestRunner::OnResponseStarted(net::URLRequest* request) {
+  // TODO(vadimt): Remove ScopedTracker below once crbug.com/422516 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "422516 ConnectionTester::TestRunner::OnResponseStarted"));
+
   if (!request->status().is_success()) {
     OnResponseCompleted(request);
     return;
@@ -354,6 +360,11 @@ void ConnectionTester::TestRunner::OnResponseStarted(net::URLRequest* request) {
 
 void ConnectionTester::TestRunner::OnReadCompleted(net::URLRequest* request,
                                                    int bytes_read) {
+  // TODO(vadimt): Remove ScopedTracker below once crbug.com/422516 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "422516 ConnectionTester::TestRunner::OnReadCompleted"));

[mmenke, 2014/11/17 15:38:16]

This file is not worth instrumenting.  It's only used from about:net-internals,
when manually triggered.  So it's not used often enough to be a common cause of
jank...And even if it were, we don't care.  That's basically internal-only API
intended for Chrome development / debugging (Not general web development).

[vadimt, 2014/11/18 01:14:27]

Done.

+
   if (bytes_read <= 0) {
     OnResponseCompleted(request);
     return;