Send an event to the page load metrics to track resource starting.

chrome/browser/page_load_metrics/page_load_tracker.cc

Index: chrome/browser/page_load_metrics/page_load_tracker.cc
diff --git a/chrome/browser/page_load_metrics/page_load_tracker.cc b/chrome/browser/page_load_metrics/page_load_tracker.cc
index 25c2883503484333a617d9ccfedb9182b6eb5e1a..ffbb54d4b005c89cbb52a232a5006d6250141bb1 100644
--- a/chrome/browser/page_load_metrics/page_load_tracker.cc
+++ b/chrome/browser/page_load_metrics/page_load_tracker.cc
@@ -561,6 +561,13 @@ bool PageLoadTracker::UpdateTiming(const PageLoadTiming& new_timing,
   return false;
 }
 
+void PageLoadTracker::OnStartedResource(
+    const ExtraRequestInfo& extra_request_info) {
+  for (const auto& observer : observers_) {
+    observer->OnStartedResource(extra_request_info);
+  }
+}
+
 void PageLoadTracker::OnLoadedResource(
     const ExtraRequestInfo& extra_request_info) {
   for (const auto& observer : observers_) {