UMA stats for stylus usage

ash/metrics/user_metrics_recorder.cc

Index: ash/metrics/user_metrics_recorder.cc
diff --git a/ash/metrics/user_metrics_recorder.cc b/ash/metrics/user_metrics_recorder.cc
index 0156819022bd5621f4a85e87c0933528b0991238..f0e75e24ab3042fa90fbd27f1bc829b15c945de2 100644
--- a/ash/metrics/user_metrics_recorder.cc
+++ b/ash/metrics/user_metrics_recorder.cc
@@ -18,10 +18,15 @@
 #include "ash/metrics/desktop_task_switch_metric_recorder.h"
 #include "ash/shell.h"
 #include "ash/wm/window_state_aura.h"
+#include "base/memory/ptr_util.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/user_metrics.h"
 #include "ui/aura/window.h"
 
+#if defined(OS_CHROMEOS)
+#include "ash/metrics/pointer_metrics_recorder.h"
+#endif
+
 namespace ash {
 
 namespace {
@@ -595,10 +600,20 @@ void UserMetricsRecorder::OnShellInitialized() {
     desktop_task_switch_metric_recorder_.reset(
         new DesktopTaskSwitchMetricRecorder());
   }
+#if defined(OS_CHROMEOS)
+  pointer_metrics_recorder_ = base::MakeUnique<PointerMetricsRecorder>();
+#endif
 }
 
 void UserMetricsRecorder::OnShellShuttingDown() {
   desktop_task_switch_metric_recorder_.reset();
+
+#if defined(OS_CHROMEOS)
+  // To clean up stylus_metrics_recorder_ properly, a valid shell instance is

[Daniel Erat, 2016/09/27 19:15:10]

nit: s/stylus/pointer/

[xiaoyinh(OOO Sep 11-29), 2016/09/29 20:37:43]

Done.

+  // required. So explicityly delete it before the shell instance becomes

[Daniel Erat, 2016/09/27 19:15:10]

nit: explicitly

[xiaoyinh(OOO Sep 11-29), 2016/09/29 20:37:43]

Done.

+  // invalid.
+  pointer_metrics_recorder_.reset();
+#endif
 }
 
 void UserMetricsRecorder::RecordPeriodicMetrics() {