Adding instrumentation to locate the source of jankiness.

content/browser/loader/resource_loader.cc

Index: content/browser/loader/resource_loader.cc
diff --git a/content/browser/loader/resource_loader.cc b/content/browser/loader/resource_loader.cc
index b462a68d038aa69ba606ff06d2fd902ae829310b..f1157bda985870c34ecd16abec8e5ca19a02e335 100644
--- a/content/browser/loader/resource_loader.cc
+++ b/content/browser/loader/resource_loader.cc
@@ -146,6 +146,11 @@ void ResourceLoader::CancelWithError(int error_code) {
 }
 
 void ResourceLoader::ReportUploadProgress() {
+  // TODO(pkasting): Remove ScopedTracker below once crbug.com/455952 is
+  // fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "455952 ResourceLoader::ReportUploadProgress"));
   if (waiting_for_upload_progress_ack_)
     return;  // Send one progress event at a time.