[Tab Metrics] Measure FP, FCP and FMP for Foreground Tab during Session Restore

chrome/browser/sessions/session_restore.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_SESSIONS_SESSION_RESTORE_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_RESTORE_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/callback_list.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "chrome/browser/sessions/session_restore_observer.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/sessions/core/session_types.h"
+#include "content/public/browser/web_contents_user_data.h"
 #include "ui/base/window_open_disposition.h"
 
 class Browser;
 class Profile;
 class SessionRestoreImpl;
 
 namespace content {
 class WebContents;
 }
 
+// Indicate the origin of the restoration of web contents (e.g., session
+// restore, reopening closed tab, and restore foreign tab). A tab
+// holds a valid instance of this class only when the tab is loading during
+// session restore.
+class RestoreOrigin : public content::WebContentsUserData<RestoreOrigin> {

[sky, 2017/07/25 16:48:00]

I think the enum makes sense if it's going to be around for the lifetime of the
WebContents, but that's not the case. You remove it at some point. How about
adding a function OnWillRestoreTab() to SessionRestoreObserver. This way
TabLoader can locally track whatever it needs to.

[chrisha, 2017/07/25 19:00:50]

+1 to this idea.

+ public:
+  enum class Type { SESSION_RESTORE };
+
+  static void CreateForWebContents(content::WebContents* contents,
+                                   RestoreOrigin::Type type);
+  static void RemoveFromWebContents(content::WebContents* contents);
+  ~RestoreOrigin() override;
+
+  Type type() const { return type_; }
+
+ private:
+  friend class content::WebContentsUserData<RestoreOrigin>;
+  explicit RestoreOrigin(Type type);
+
+  Type type_;
+};
+
 // SessionRestore handles restoring either the last or saved session. Session
 // restore come in two variants, asynchronous or synchronous. The synchronous
 // variety is meant for startup and blocks until restore is complete.
 class SessionRestore {
  public:
   // Bitmask representing behaviors available when restoring a session. Populate
   // using the values below.
   using BehaviorBitmask = uint32_t;
 
   enum {
@@ skipping 115 matching lines @@
   // Contains all registered observers for session restore events.
   static SessionRestoreObserverList* observers_;
 
   // Whether session restore started or not.
   static bool session_restore_started_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionRestore);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_SESSION_RESTORE_H_