Adding previews information to PLM UKM

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 da136446f1be385320329e089ca648ebd0208d6d..bc10adb0a872142b59f4191728d6d380bb1ce6bb 100644
--- a/chrome/browser/page_load_metrics/page_load_tracker.cc
+++ b/chrome/browser/page_load_metrics/page_load_tracker.cc
@@ -639,4 +639,10 @@ void PageLoadTracker::OnSubframeMetadataChanged() {
   }
 }
 
+void PageLoadTracker::BroadcastEventToObservers(const void* const event_key) {
+  for (const auto& observer : observers_) {
+    observer->OnEventOccurred(event_key);
+  }
+}
+
 }  // namespace page_load_metrics