add stylus metrics

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 505e943e336ea8cda7d0bb667d8638340b9e2284..33ced2ef402428d468238c8a9cf622420793486a 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -128,6 +128,7 @@
 #include "ash/system/chromeos/power/video_activity_notifier.h"
 #include "ash/touch/touch_transformer_controller.h"
 #include "ash/virtual_keyboard_controller.h"
+#include "ash/wm/stylus_metrics_recorder.h"
 #include "base/bind_helpers.h"
 #include "base/sys_info.h"
 #include "chromeos/audio/audio_a11y_controller.h"
@@ -552,6 +553,9 @@ Shell::~Shell() {
   RemovePostTargetHandler(toplevel_window_event_handler_.get());
   RemovePreTargetHandler(system_gesture_filter_.get());
   RemovePreTargetHandler(mouse_cursor_filter_.get());
+#if defined(OS_CHROMEOS)
+  RemovePreTargetHandler(stylus_metrics_recorder_.get());
+#endif
   RemovePreTargetHandler(modality_filter_.get());
 
   // TooltipController is deleted with the Shell so removing its references.
@@ -640,9 +644,7 @@ Shell::~Shell() {
 
 #if defined(OS_CHROMEOS)
   touch_transformer_controller_.reset();
-#endif  // defined(OS_CHROMEOS)
-
-#if defined(OS_CHROMEOS)
+  stylus_metrics_recorder_.reset();
   audio_a11y_controller_.reset();
 #endif  // defined(OS_CHROMEOS)
 
@@ -864,6 +866,14 @@ void Shell::Init(const ShellInitParams& init_params) {
   mouse_cursor_filter_.reset(new MouseCursorEventFilter());
   PrependPreTargetHandler(mouse_cursor_filter_.get());
 
+#if defined(OS_CHROMEOS)
+  // |stylus_metrics_recorder| records stylus metrics for certain events.
+  // It does not handle/consume any events, so prepend it as a pre-target hander
+  // before events are consumed elsewhere.
+  stylus_metrics_recorder_.reset(new StylusMetricsRecorder());
+  PrependPreTargetHandler(stylus_metrics_recorder_.get());
+#endif
+
   // Create Controllers that may need root window.
   // TODO(oshima): Move as many controllers before creating
   // RootWindowController as possible.