Report user actions when gesture starts and stops in user_model.

components/scheduler/renderer/user_model.cc

Index: components/scheduler/renderer/user_model.cc
diff --git a/components/scheduler/renderer/user_model.cc b/components/scheduler/renderer/user_model.cc
index c71e86c21d8e20f63ab20981964971f4639a08d4..87c7e1f0d52fc23b7198aa765f37549c2fb2ea37 100644
--- a/components/scheduler/renderer/user_model.cc
+++ b/components/scheduler/renderer/user_model.cc
@@ -5,6 +5,8 @@
 #include "components/scheduler/renderer/user_model.h"
 
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/user_metrics.h"
+#include "base/single_thread_task_runner.h"
 
 namespace scheduler {
 
@@ -26,10 +28,24 @@ void RecordGesturePrediction(GesturePredictionResult result) {
 
 }  // namespace
 
-UserModel::UserModel()
-    : pending_input_event_count_(0),
+namespace features {
+
+// Enables the recording of gesture as UMA user actions.

[Ilya Sherman, 2016/03/21 08:09:43]

nit: s/gesture/gestures

[beaudoin, 2016/03/23 02:46:41]

Done.

+// That feature is disabled by default and controlled from the server so as not
+// to generate too many UMA user actions.
+const base::Feature kRecordGestureAction {"RecordGestureActions",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
+}  // namespace features
+
+UserModel::UserModel(
+    const scoped_refptr<base::SingleThreadTaskRunner>& default_task_runner)
+    : default_task_runner_(default_task_runner),
+      pending_input_event_count_(0),
       is_gesture_active_(false),
-      is_gesture_expected_(false) {}
+      is_gesture_expected_(false),
+      record_gesture_action_(

[Ilya Sherman, 2016/03/21 08:09:43]

Hmm, why do you need to cache this state?  base::FeatureList::IsEnabled() should
be pretty efficient.  Did you find that it's not sufficiently efficient for your
needs?

[alex clarke (OOO till 29th), 2016/03/21 09:27:26]

Because I asked him to:)  The UserModel gets evaluated quite a bit so I don't
want to do unnecessary work when we could cache it.

[beaudoin, 2016/03/23 02:46:41]

Suggest leaving it like that for now. I've added a comment.

[Ilya Sherman, 2016/03/24 05:02:35]

the base::FeatureList::IsEnabled() call is basically a single map lookup.  Is
your code really so performance-sensitive?  IMO this seems like premature
optimization which hurts readability.

+          base::FeatureList::IsEnabled(features::kRecordGestureAction)) {}
 UserModel::~UserModel() {}
 
 void UserModel::DidStartProcessingInputEvent(blink::WebInputEvent::Type type,
@@ -42,6 +58,14 @@ void UserModel::DidStartProcessingInputEvent(blink::WebInputEvent::Type type,
     if (!is_gesture_active_) {
       last_gesture_start_time_ = now;
 
+      if (record_gesture_action_) {
+        default_task_runner_->PostTask(
+            FROM_HERE,
+            base::Bind(&base::RecordAction,
+                       base::UserMetricsAction(
+                           "RendererScheduler.UserModel.GestureStart")));
+      }
+
       RecordGesturePrediction(is_gesture_expected_
                                   ? GESTURE_OCCURED_WAS_PREDICTED
                                   : GESTURE_OCCURED_BUT_NOT_PREDICTED);
@@ -91,6 +115,13 @@ void UserModel::DidStartProcessingInputEvent(blink::WebInputEvent::Type type,
       base::TimeDelta duration = now - last_gesture_start_time_;
       UMA_HISTOGRAM_TIMES("RendererScheduler.UserModel.GestureDuration",
                           duration);
+      if (record_gesture_action_) {
+        default_task_runner_->PostTask(
+            FROM_HERE,
+            base::Bind(&base::RecordAction,
+                       base::UserMetricsAction(
+                           "RendererScheduler.UserModel.GestureEnd")));
+      }
     }
     is_gesture_active_ = false;
   }