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 624c3f5eab685a3b49e76fa55b08ef5e57b6c544..81607cc96669f5495830ce955dcdafd967192837 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.cc
@@ -100,6 +100,10 @@
 #include "ui/resources/grit/ui_resources.h"
 #include "ui/wm/core/window_animations.h"
 
+#if defined(OS_CHROMEOS)
+#include "chrome/browser/ui/ash/metrics/stylus_metrics_recorder_chromeos.h"
+#endif
+
 using extensions::Extension;
 using extensions::UnloadedExtensionInfo;
 using extension_misc::kGmailAppId;
@@ -877,9 +881,20 @@ 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) {
+#if defined(OS_CHROMEOS)
+  // To clean up stylus_metrics_recorder_ properly, a valid shell instance is
+  // required. So explicityly delete it before the shell instance becomes
+  // invalid.
+  stylus_metrics_recorder_.reset();
+#endif
+}
 
 void ChromeLauncherControllerImpl::OnShelfAlignmentChanged(
     ash::WmShelf* shelf) {