[Sessions] Add detailed logging of SessionRestore events.

chrome/browser/sessions/tab_loader.cc

Index: chrome/browser/sessions/tab_loader.cc
diff --git a/chrome/browser/sessions/tab_loader.cc b/chrome/browser/sessions/tab_loader.cc
index bf1b00a0258d2b777399dc95c5984891bc02b319..bee50bcb8f00619a1a9ece6498a876866ef3f4b9 100644
--- a/chrome/browser/sessions/tab_loader.cc
+++ b/chrome/browser/sessions/tab_loader.cc
@@ -9,6 +9,7 @@
 
 #include "base/metrics/histogram.h"
 #include "base/strings/stringprintf.h"
+#include "chrome/browser/sessions/session_restore_stats_collector.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
@@ -214,9 +215,17 @@ void TabLoader::OnMemoryPressure(
   // Stop the timer and suppress any tab loads while we clean the list.
   SetTabLoadingEnabled(false);
   while (!tabs_to_load_.empty()) {
-    NavigationController* controller = tabs_to_load_.front();
+    NavigationController* tab = tabs_to_load_.front();
     tabs_to_load_.pop_front();
-    RemoveTab(controller);
+    RemoveTab(tab);
+
+    // Notify the stats collector that a tab's loading has been deferred due to
+    // memory pressure. It's possible for the stats collector to infer this on
+    // its own, but not in the presence of the above experiment, hence this is
+    // explicitly called.
+    // TODO(chrisha): Re-evaluate this was the memory-pressure experiment is
+    // finished.
+    SessionRestoreStatsCollector::DeferTab(tab);
   }
   // By calling |LoadNextTab| explicitly, we make sure that the
   // |NOTIFICATION_SESSION_RESTORE_DONE| event gets sent.