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

chrome/browser/resource_coordinator/tab_manager.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_RESOURCE_COORDINATOR_TAB_MANAGER_H_
 #define CHROME_BROWSER_RESOURCE_COORDINATOR_TAB_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 166 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, IsInternalPage);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, OomPressureListener);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectPDFPages);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectRecentlyUsedTabs);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ProtectVideoTabs);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, ReloadDiscardedTabContextMenu);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, TabManagerBasics);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, FastShutdownSingleTabProcess);
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest,
                            GetUnsortedTabStatsIsInVisibleWindow);
+  FRIEND_TEST_ALL_PREFIXES(TabManagerTest, HistogramsSessionRestoreSwitchToTab);
 
   // Information about a Browser.
   struct BrowserInfo {
     TabStripModel* tab_strip_model;
     bool window_is_active;
     bool window_is_minimized;
     gfx::Rect window_bounds;
     bool browser_is_app;
   };
 
@@ skipping 126 matching lines @@
   // Returns true if tabs can be discarded only once.
   bool CanOnlyDiscardOnce() const;
 
   // Returns a list of BrowserInfo sorted in z-order from top to bottom. The
   // list is constructed from either |test_browser_info_list_| or BrowserList.
   std::vector<BrowserInfo> GetBrowserInfoList() const;
 
   void OnSessionRestoreStartedLoadingTabs();
   void OnSessionRestoreFinishedLoadingTabs();
 
+  // Records UMA histograms for the tab state when switching to a different tab
+  // during session restore and background tab loading.
+  //
+  // TODO(shaseley): Add background tab loading stats when it gets integrated

[lpy, 2017/06/27 22:30:36]

Merge this TODO into the one in .cc, it doesn't give any information along with
the API.

[shaseley, 2017/06/27 23:22:10]

Per fmeawad@'s comment, I was planning to remove the one in the .cc. Is it OK to
just remove both since the code is consistent as is?

+  // into the TabManager.
+  void RecordSwitchToTab(content::WebContents* contents) const;
+
   // Timer to periodically update the stats of the renderers.
   base::RepeatingTimer update_timer_;
 
   // Timer to periodically report whether a tab has been discarded since the
   // last time the timer has fired.
   base::RepeatingTimer recent_tab_discard_timer_;
 
   // A listener to global memory pressure events.
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
@@ skipping 56 matching lines @@
 
   // Weak pointer factory used for posting delayed tasks.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace resource_coordinator
 
 #endif  // CHROME_BROWSER_RESOURCE_COORDINATOR_TAB_MANAGER_H_