[Sessions] Add detailed logging of SessionRestore events.

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 5a9cb08035a7b0a18f427b2f8f229a7b2b1c2177..353f37bb6ccdd7b3690b2fefb655ba2a43e693b6 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -35,6 +35,7 @@
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
+#include "content/public/browser/session_restore_uma.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/common/content_client.h"
@@ -1750,8 +1751,24 @@ size_t NavigationControllerImpl::max_entry_count() {
 }
 
 void NavigationControllerImpl::SetActive(bool is_active) {
-  if (is_active && needs_reload_)
+  if (is_active && needs_reload_) {
+    // If the pending navigation is a session restore entry then it is being
+    // loaded because of user action, and not automatically by the TabLoader.
+    // Consider this a deferred reload that the user then forced to occur.
+    // Better session restore tab prioritization should reduce the number of
+    // times this occurs.
+    NavigationEntryImpl* pending_entry =
+        entries_[last_committed_entry_index_].get();
+    if (pending_entry->restore_type() == RESTORE_LAST_SESSION_EXITED_CLEANLY ||
+        pending_entry->restore_type() == RESTORE_LAST_SESSION_CRASHED) {
+      UMA_HISTOGRAM_ENUMERATION(
+          content::kSessionRestoreTabActions,
+          content::kSessionRestoreTabActionsUma_DeferredTabLoadedByUserAction,
+          content::kSessionRestoreTabActionsUma_Max);
+    }
+
     LoadIfNecessary();
+  }
 }
 
 void NavigationControllerImpl::LoadIfNecessary() {