[TabMetrics] Add signals that mark the start and end of session restore.

chrome/browser/sessions/tab_loader.cc

Index: chrome/browser/sessions/tab_loader.cc
diff --git a/chrome/browser/sessions/tab_loader.cc b/chrome/browser/sessions/tab_loader.cc
index 753f4e0493c23ad66dc15e7f1f37a6574ce3f7e1..211073f76a9c3bf07828438cd8a69438f251e798 100644
--- a/chrome/browser/sessions/tab_loader.cc
+++ b/chrome/browser/sessions/tab_loader.cc
@@ -13,6 +13,8 @@
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/resource_coordinator/tab_manager.h"
 #include "chrome/browser/sessions/session_restore_stats_collector.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
@@ -103,6 +105,7 @@ TabLoader::TabLoader(base::TimeTicks restore_started)
   shared_tab_loader_ = this;
   this_retainer_ = this;
   base::MemoryCoordinatorClientRegistry::GetInstance()->Register(this);
+  MarkSessionRestoreStarted();
 }
 
 TabLoader::~TabLoader() {
@@ -110,6 +113,7 @@ TabLoader::~TabLoader() {
   DCHECK(shared_tab_loader_ == this);
   shared_tab_loader_ = nullptr;
   base::MemoryCoordinatorClientRegistry::GetInstance()->Unregister(this);
+  MarkSessionRestoreEnded();
 }
 
 void TabLoader::StartLoading(const std::vector<RestoredTab>& tabs) {
@@ -313,5 +317,21 @@ void TabLoader::StopLoadingTabs() {
   LoadNextTab();
 }
 
+// static
+void TabLoader::MarkSessionRestoreStarted() {
+  resource_coordinator::TabManager* tab_manager =
+      g_browser_process->GetTabManager();
+  DCHECK(tab_manager);
+  tab_manager->MarkSessionRestoreStarted();
+}
+
+// static
+void TabLoader::MarkSessionRestoreEnded() {
+  resource_coordinator::TabManager* tab_manager =
+      g_browser_process->GetTabManager();
+  DCHECK(tab_manager);
+  tab_manager->MarkSessionRestoreEnded();
+}
+
 // static
 TabLoader* TabLoader::shared_tab_loader_ = nullptr;