UMA stats for stylus usage

chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc

Index: chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
diff --git a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
index 66fc3b85a2e3f5291e5506d1d33a1e03db5ea378..48c48f08121ed231adf7694e1febb54728d37fb5 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
@@ -877,9 +877,19 @@ void ChromeLauncherControllerImpl::OnShelfCreated(ash::WmShelf* shelf) {
 
   if (ash::ShelfWidget::ShelfAlignmentAllowed())
     shelf->SetAlignment(ash::launcher::GetShelfAlignmentPref(prefs, display));
+#if defined(OS_CHROMEOS)
+  stylus_metrics_recorder_ =
+      base::MakeUnique<chromeos::StylusMetricsRecorder>();
+#endif
 }
 
-void ChromeLauncherControllerImpl::OnShelfDestroyed(ash::WmShelf* shelf) {}
+void ChromeLauncherControllerImpl::OnShelfDestroyed(ash::WmShelf* shelf) {
+// To clean up stylus_metrics_recorder_ properly, a valid shell instance is
+// required. So explicityly delete it before the shell instance becomes invalid.

[xiyuan, 2016/09/16 20:07:54]

nit: wrong indent. Comment should use the same indent as code.

[xiaoyinh(OOO Sep 11-29), 2016/09/16 22:34:25]

Done.

+#if defined(OS_CHROMEOS)

[xiyuan, 2016/09/16 20:07:54]

nit: move this above the comment to keep it closer to code.

[xiaoyinh(OOO Sep 11-29), 2016/09/16 22:34:25]

Done.

+  stylus_metrics_recorder_.reset();
+#endif
+}
 
 void ChromeLauncherControllerImpl::OnShelfAlignmentChanged(
     ash::WmShelf* shelf) {