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

chrome/browser/resource_coordinator/tab_manager_unittest.cc

Index: chrome/browser/resource_coordinator/tab_manager_unittest.cc
diff --git a/chrome/browser/resource_coordinator/tab_manager_unittest.cc b/chrome/browser/resource_coordinator/tab_manager_unittest.cc
index 238610c99fd9b59476d9d3d0e6fa86bf0d2c2cee..128e305ba67812fcbde5029ecf8900832b452f17 100644
--- a/chrome/browser/resource_coordinator/tab_manager_unittest.cc
+++ b/chrome/browser/resource_coordinator/tab_manager_unittest.cc
@@ -14,6 +14,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string16.h"
+#include "base/test/histogram_tester.h"
 #include "base/test/mock_entropy_provider.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "base/time/time.h"
@@ -601,4 +602,50 @@ TEST_F(TabManagerTest, OnSessionRestoreStartedAndFinishedLoadingTabs) {
   EXPECT_FALSE(tab_manager->IsSessionRestoreLoadingTabs());
 }
 
+TEST_F(TabManagerTest, HistogramsSessionRestoreSwitchToTab) {
+  const char kHistogramName[] = "TabManager.SessionRestore.SwitchToTab";
+
+  TabManager tab_manager;
+  WebContents* tab = CreateWebContents();
+  auto* data = tab_manager.GetWebContentsData(tab);
+
+  base::HistogramTester histograms;
+  histograms.ExpectTotalCount(kHistogramName, 0);
+
+  data->SetTabLoadingState(TAB_IS_LOADING);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+
+  // Nothing should happen until we're in a session restore
+  histograms.ExpectTotalCount(kHistogramName, 0);
+
+  tab_manager.OnSessionRestoreStartedLoadingTabs();
+
+  data->SetTabLoadingState(TAB_IS_NOT_LOADING);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+  histograms.ExpectTotalCount(kHistogramName, 2);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_NOT_LOADING, 2);
+
+  data->SetTabLoadingState(TAB_IS_LOADING);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+
+  histograms.ExpectTotalCount(kHistogramName, 5);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_NOT_LOADING, 2);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_LOADING, 3);
+
+  data->SetTabLoadingState(TAB_IS_LOADED);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+  tab_manager.RecordSwitchToTab(tab);
+
+  histograms.ExpectTotalCount(kHistogramName, 9);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_NOT_LOADING, 2);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_LOADING, 3);
+  histograms.ExpectBucketCount(kHistogramName, TAB_IS_LOADED, 4);
+}
+
 }  // namespace resource_coordinator