Adding instrumentation to locate the source of jankiness.

net/proxy/polling_proxy_config_service.cc

Index: net/proxy/polling_proxy_config_service.cc
diff --git a/net/proxy/polling_proxy_config_service.cc b/net/proxy/polling_proxy_config_service.cc
index 611ea5975c094621ca926a6fd779c0242dc2cced..7c086db3b89b7b82826e8cf48b79fa59e7650ad5 100644
--- a/net/proxy/polling_proxy_config_service.cc
+++ b/net/proxy/polling_proxy_config_service.cc
@@ -9,6 +9,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/observer_list.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/worker_pool.h"
 #include "net/proxy/proxy_config.h"
@@ -113,6 +114,11 @@ class PollingProxyConfigService::Core
 
   // Called after the worker thread has finished retrieving a configuration.
   void GetConfigCompleted(const ProxyConfig& config) {
+    // TODO(pkasting): Remove ScopedTracker below once crbug.com/455942 is
+    // fixed.
+    tracked_objects::ScopedTracker tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "455942 PollingProxyConfigService::Core::GetConfigCompleted"));
     DCHECK(poll_task_outstanding_);
     poll_task_outstanding_ = false;