[Tab Metrics] Added TabManager.SessionRestore.SwitchToTab UMA.

chrome/browser/resource_coordinator/tab_manager.h

Index: chrome/browser/resource_coordinator/tab_manager.h
diff --git a/chrome/browser/resource_coordinator/tab_manager.h b/chrome/browser/resource_coordinator/tab_manager.h
index 414b743c8426e5c474210a5a3600db6db3841f95..6892bdddbf4c456550188307dd033f30966b9950 100644
--- a/chrome/browser/resource_coordinator/tab_manager.h
+++ b/chrome/browser/resource_coordinator/tab_manager.h
@@ -184,6 +184,7 @@ class TabManager : public TabStripModelObserver {
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, FastShutdownSingleTabProcess);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest,
                            GetUnsortedTabStatsIsInVisibleWindow);
+  FRIEND_TEST_ALL_PREFIXES(TabManagerTest, HistogramsSessionRestoreSwitchToTab);
 
   // Information about a Browser.
   struct BrowserInfo {
@@ -330,6 +331,10 @@ class TabManager : public TabStripModelObserver {
   void OnSessionRestoreStartedLoadingTabs();
   void OnSessionRestoreFinishedLoadingTabs();
 
+  // Records UMA histograms for the tab state when switching to a different tab
+  // during session restore.
+  void RecordSwitchToTab(content::WebContents* contents) const;
+
   // Timer to periodically update the stats of the renderers.
   base::RepeatingTimer update_timer_;