Make PageLoadMetricsObserver::OnStart return ObservePolicy

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index 1ca66e37badf183e35d83311e16ae78205437a41..4b7cf31162801e0b353c4e2dcd647afe4309e655 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -325,10 +325,8 @@ PageLoadTracker::PageLoadTracker(
   }
 
   embedder_interface_->RegisterObservers(this);
-  for (const auto& observer : observers_) {
-    observer->OnStart(navigation_handle, currently_committed_url,
-                      started_in_foreground_);
-  }
+  INVOKE_AND_PRUNE_OBSERVERS(observers_, OnStart, navigation_handle,
+                             currently_committed_url, started_in_foreground_);
 }
 
 PageLoadTracker::~PageLoadTracker() {