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

chrome/browser/sessions/session_restore.h

Index: chrome/browser/sessions/session_restore.h
diff --git a/chrome/browser/sessions/session_restore.h b/chrome/browser/sessions/session_restore.h
index 17090a514c97928dc4fa5ebbe29d7e4b60d7986a..3e5229198e19e32aa38925e2e3c8adef4106b8c4 100644
--- a/chrome/browser/sessions/session_restore.h
+++ b/chrome/browser/sessions/session_restore.h
@@ -17,6 +17,7 @@
 #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;
@@ -27,6 +28,28 @@ 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.