Added the Ash.Tab.TimeBetweenSwitchToExistingTabUserActions histogram to track time between tab swit

chrome/browser/ui/views/tabs/tab_strip.cc

Index: chrome/browser/ui/views/tabs/tab_strip.cc
diff --git a/chrome/browser/ui/views/tabs/tab_strip.cc b/chrome/browser/ui/views/tabs/tab_strip.cc
index 10958ee6a805b1738e3bda9d1306ab5b12204ec0..cfc64b594924e19983918faa3ad6aac0fcbe78fe 100644
--- a/chrome/browser/ui/views/tabs/tab_strip.cc
+++ b/chrome/browser/ui/views/tabs/tab_strip.cc
@@ -2629,6 +2629,7 @@ void TabStrip::SetResetToShrinkOnExit(bool value) {
 void TabStrip::ButtonPressed(views::Button* sender, const ui::Event& event) {
   if (sender == newtab_button_) {
     content::RecordAction(UserMetricsAction("NewTab_Button"));
+    // TODO(bruthig):
     UMA_HISTOGRAM_ENUMERATION("Tab.NewTab", TabStripModel::NEW_TAB_BUTTON,
                               TabStripModel::NEW_TAB_ENUM_COUNT);
     if (event.IsMouseEvent()) {
@@ -2735,6 +2736,7 @@ void TabStrip::OnGestureEvent(ui::GestureEvent* event) {
       if (active_tab->tab_activated_with_last_tap_down())
         action = TouchUMA::GESTURE_TABSWITCH_TAP;
       TouchUMA::RecordGestureAction(action);
+      // TODO(bruthig):
       break;
     }