Add support for counting same-document AMP loads.

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 9b37f75a0629d1416d43c1b706e4e3141e04dbc1..ea73276dd941b2e984ddeb95b24b6ddfc77d1733 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -336,6 +336,8 @@ void MetricsWebContentsObserver::DidFinishNavigation(
       navigation_handle->IsSameDocument()) {
     if (finished_nav)
       finished_nav->StopTracking();
+    if (committed_load_)
+      committed_load_->DidCommitSameDocumentNavigation(navigation_handle);
     return;
   }