UMA stats for stylus usage

ash/metrics/user_metrics_recorder.h

Index: ash/metrics/user_metrics_recorder.h
diff --git a/ash/metrics/user_metrics_recorder.h b/ash/metrics/user_metrics_recorder.h
index 37cb26e685345c4c7f7f9b175c3d197e47394d67..e2aca6699597b83cc76c411fd8ff70ee480f72f6 100644
--- a/ash/metrics/user_metrics_recorder.h
+++ b/ash/metrics/user_metrics_recorder.h
@@ -17,6 +17,10 @@ namespace ash {
 
 class DesktopTaskSwitchMetricRecorder;
 
+#if defined(OS_CHROMEOS)
+class PointerMetricsRecorder;
+#endif
+
 namespace test {
 class UserMetricsRecorderTestAPI;
 }
@@ -78,6 +82,11 @@ class ASH_EXPORT UserMetricsRecorder {
   std::unique_ptr<DesktopTaskSwitchMetricRecorder>
       desktop_task_switch_metric_recorder_;
 
+#if defined(OS_CHROMEOS)
+  // Metric recorder to track pointer down events.
+  std::unique_ptr<PointerMetricsRecorder> pointer_metrics_recorder_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(UserMetricsRecorder);
 };