Adding instrumentation to locate the source of jankiness.

chrome/browser/net/pref_proxy_config_tracker_impl.cc

Index: chrome/browser/net/pref_proxy_config_tracker_impl.cc
diff --git a/chrome/browser/net/pref_proxy_config_tracker_impl.cc b/chrome/browser/net/pref_proxy_config_tracker_impl.cc
index 3e969c8bbc22277cced45dfd1b53b507ecc98849..6e9b771c466a7806cf2b2b0fad95a1a3dfc92f0e 100644
--- a/chrome/browser/net/pref_proxy_config_tracker_impl.cc
+++ b/chrome/browser/net/pref_proxy_config_tracker_impl.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/values.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/prefs/proxy_config_dictionary.h"
@@ -101,6 +102,10 @@ void ChromeProxyConfigService::UpdateProxyConfig(
 void ChromeProxyConfigService::OnProxyConfigChanged(
     const net::ProxyConfig& config,
     ConfigAvailability availability) {
+  // TODO(pkasting): Remove ScopedTracker below once crbug.com/455942 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "455942 ChromeProxyConfigService::OnProxyConfigChanged"));
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
   // Check whether there is a proxy configuration defined by preferences. In