[Sessions] Add detailed logging of SessionRestore events.

chrome/browser/sessions/session_restore_stats_collector.h

Index: chrome/browser/sessions/session_restore_stats_collector.h
diff --git a/chrome/browser/sessions/session_restore_stats_collector.h b/chrome/browser/sessions/session_restore_stats_collector.h
index c312b404383a4530c356063b8acd35f0cd2ed9fd..54d740143b9dc68f1f3a2084be97fef167c4bf86 100644
--- a/chrome/browser/sessions/session_restore_stats_collector.h
+++ b/chrome/browser/sessions/session_restore_stats_collector.h
@@ -5,6 +5,7 @@
 #ifndef CHROME_BROWSER_SESSIONS_SESSION_RESTORE_STATS_COLLECTOR_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_RESTORE_STATS_COLLECTOR_H_
 
+#include <map>
 #include <set>
 
 #include "base/callback_list.h"
@@ -30,6 +31,11 @@ class SessionRestoreStatsCollector
       const std::vector<SessionRestoreDelegate::RestoredTab>& tabs,
       const base::TimeTicks& restore_started);
 
+  // Called to indicate that the loading of a tab has been deferred by session
+  // restore. If the reason for the deferral was memory pressure this will be
+  // recorded.
+  static void DeferTab(content::NavigationController* tab);
+
  private:
   friend class base::RefCounted<SessionRestoreStatsCollector>;
 
@@ -46,8 +52,13 @@ class SessionRestoreStatsCollector
   // Adds new tabs to the list of tracked tabs.
   void AddTabs(const std::vector<SessionRestoreDelegate::RestoredTab>& tabs);
 
-  // Called when a tab is no longer tracked.
-  void RemoveTab(content::NavigationController* tab);
+  // Called to indicate that the loading of a tab has been deferred by session
+  // restore. Called by the static DeferTab.
+  void DeferTabImpl(content::NavigationController* tab);
+
+  // Called when a tab is no longer tracked. This is called by the 'Observe'
+  // notification callback.
+  void RemoveTab(bool is_deferred, content::NavigationController* tab);
 
   // Registers for relevant notifications for a tab.
   void RegisterForNotifications(content::NavigationController* tab);
@@ -56,6 +67,10 @@ class SessionRestoreStatsCollector
   content::RenderWidgetHost* GetRenderWidgetHost(
       content::NavigationController* tab);
 
+  // Returns true if the specified tab had it's loading deferred by an active
+  // session restore.
+  bool IsDeferred(content::NavigationController* tab);
+
   // Have we recorded the times for a foreground tab load?
   bool got_first_foreground_load_;
 
@@ -71,12 +86,30 @@ class SessionRestoreStatsCollector
   // The renderers we have loaded and are waiting on to paint.
   RenderWidgetHostSet render_widget_hosts_to_paint_;
 
-  // List of tracked tabs.
-  std::set<content::NavigationController*> tabs_tracked_;
+  // List of tracked tabs. Each tab is associated with the automatically
+  // assigned ID of the ongoing session restore that created the tab.
+  std::map<content::NavigationController*, int> tabs_tracked_;
+
+  // List of deferred tabs. Each tab is associated with its session restore ID,
+  // as with tabs_tracked_.
+  std::map<content::NavigationController*, int> tabs_deferred_;
 
-  // The number of tabs that have been restored.
+  // A set of session restore IDs that have had tabs deferred. Absence from this
+  // set means the session restore did not defer any tabs.
+  std::set<int> deferred_tabs_seen_;
+
+  // The number of tabs that have been restored. This is across all overlapping
+  // session restores.
   int tab_count_;
 
+  // The number of tabs that have been deferred. This is across all overlapping
+  // session restores.
+  int tab_deferred_count_;
+
+  // The ID of the most recently initiated session restore. Incremented by
+  // calls to AddTabs.
+  int session_restore_id_;
+
   // Max number of tabs that were loaded in parallel (for metrics).
   size_t max_parallel_tab_loads_;