Added metrics to track the time between task switches done via Alt+Tab and Alt+Shift+Tab.

ash/wm/window_cycle_controller.cc

Index: ash/wm/window_cycle_controller.cc
diff --git a/ash/wm/window_cycle_controller.cc b/ash/wm/window_cycle_controller.cc
index 42f866e38e0ab17e7ba7cb39ea2e47d6b41e68a0..98f93391c27b009d25e92cb65095bab72bc69fdc 100644
--- a/ash/wm/window_cycle_controller.cc
+++ b/ash/wm/window_cycle_controller.cc
@@ -4,11 +4,13 @@
 
 #include "ash/wm/window_cycle_controller.h"
 
+#include "ash/metrics/user_metrics_recorder.h"
 #include "ash/session/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/window_cycle_list.h"
 #include "base/metrics/histogram.h"
+#include "ui/aura/window.h"
 #include "ui/events/event.h"
 #include "ui/events/event_handler.h"
 
@@ -16,6 +18,12 @@ namespace ash {
 
 namespace {
 
+// Returns the most recently active window from the |window_list| or nullptr
+// if the list is empty.
+aura::Window* GetActiveWindow(const MruWindowTracker::WindowList& window_list) {
+  return window_list.size() > 0 ? window_list[0] : nullptr;

[Alexei Svitkine (slow), 2015/05/14 20:42:14]

Nit: .size() > 0 -> !.empty()

[bruthig, 2015/05/14 22:06:40]

Done.

+}
+
 // Filter to watch for the termination of a keyboard gesture to cycle through
 // multiple windows.
 class WindowCycleEventFilter : public ui::EventHandler {
@@ -77,8 +85,12 @@ void WindowCycleController::HandleCycleWindow(Direction direction) {
 }
 
 void WindowCycleController::StartCycling() {
-  window_cycle_list_.reset(new WindowCycleList(ash::Shell::GetInstance()->
-      mru_window_tracker()->BuildMruWindowList()));
+  MruWindowTracker::WindowList window_list =
+      Shell::GetInstance()->mru_window_tracker()->BuildMruWindowList();
+
+  active_window_before_window_cycle_ = GetActiveWindow(window_list);

[oshima, 2015/05/14 17:12:36]

doesn't GetActiveWindow work here?

[bruthig, 2015/05/14 17:49:44]

Summary of discussion offline.

wm::GetActiveWindow() can return transient windows for things like the status
tray which are not included in the definition of a "Task".  So this is
intentionally comparing the last active window that is also choose-able via
Alt+Tab.

Will leave it as-is.

[oshima, 2015/05/14 18:13:00]

Acknowledged.

+
+  window_cycle_list_.reset(new WindowCycleList(window_list));
   event_handler_.reset(new WindowCycleEventFilter());
   cycle_start_time_ = base::Time::Now();
   Shell::GetInstance()->metrics()->RecordUserMetricsAction(UMA_WINDOW_CYCLE);
@@ -94,10 +106,23 @@ void WindowCycleController::Step(Direction direction) {
 
 void WindowCycleController::StopCycling() {
   window_cycle_list_.reset();
+
+  aura::Window* active_window_after_window_cycle = GetActiveWindow(
+      Shell::GetInstance()->mru_window_tracker()->BuildMruWindowList());
+
   // Remove our key event filter.
   event_handler_.reset();
   UMA_HISTOGRAM_MEDIUM_TIMES("Ash.WindowCycleController.CycleTime",
                              base::Time::Now() - cycle_start_time_);
+
+  if (active_window_after_window_cycle != nullptr &&
+      active_window_before_window_cycle_ != active_window_after_window_cycle) {
+    Shell::GetInstance()
+        ->metrics()
+        ->task_switch_metrics_recorder()
+        .OnTaskSwitch(TaskSwitchMetricsRecorder::kWindowCycleController);
+  }
+  active_window_before_window_cycle_ = nullptr;
 }
 
 }  // namespace ash