Add support for counting same-document AMP loads.

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 77d31f62cb34f6d1d91ea4d8c66f759988976674..7c6318e8fa9e924ce49f71b24a8a9cd3fa224339 100644
--- a/chrome/browser/page_load_metrics/page_load_tracker.cc
+++ b/chrome/browser/page_load_metrics/page_load_tracker.cc
@@ -551,10 +551,18 @@ void PageLoadTracker::Commit(content::NavigationHandle* navigation_handle) {
   LogAbortChainHistograms(navigation_handle);
 }
 
+void PageLoadTracker::DidCommitSameDocumentNavigation(
+    content::NavigationHandle* navigation_handle) {
+  for (const auto& observer : observers_) {
+    observer->OnCommitSameDocumentNavigation(navigation_handle);
+  }
+}
+
 void PageLoadTracker::DidFinishSubFrameNavigation(
     content::NavigationHandle* navigation_handle) {
-  INVOKE_AND_PRUNE_OBSERVERS(observers_, OnDidFinishSubFrameNavigation,
-                             navigation_handle);
+  for (const auto& observer : observers_) {
+    observer->OnDidFinishSubFrameNavigation(navigation_handle);
+  }
 
   if (!navigation_handle->HasCommitted())
     return;