Adds UMA for screen rotation animation smoothness.

ash/rotator/screen_rotation_animator.cc

Index: ash/rotator/screen_rotation_animator.cc
diff --git a/ash/rotator/screen_rotation_animator.cc b/ash/rotator/screen_rotation_animator.cc
index c0dbe2058d6f7a4c33314ed1f07650cde2446195..ef7f54464fb94a9d9dc8f46f9edc9edd18618262 100644
--- a/ash/rotator/screen_rotation_animator.cc
+++ b/ash/rotator/screen_rotation_animator.cc
@@ -14,6 +14,7 @@
 #include "ash/shell.h"
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
@@ -47,6 +48,10 @@ const int kRotationDurationInMs = 250;
 const int kCounterClockWiseRotationFactor = 1;
 const int kClockWiseRotationFactor = -1;
 
+// The percentage histogram boundary.
+const int kPercentage_MIN = 1;
+const int kPercentage_MAX = 101;
+
 // Aborts the active animations of the layer, and recurses upon its child
 // layers.
 void AbortAnimations(ui::Layer* layer) {
@@ -177,9 +182,21 @@ struct ScreenRotationAnimator::ScreenRotationRequest {
   display::Display::RotationSource source;
 };
 
+class ScreenRotationAnimator::ScreenRotationAnimationMetricsReporter
+    : public ui::AnimationMetricsReporter {
+  void Report(int value) override {
+    base::LinearHistogram::FactoryGet(
+        "Ash.Rotation.AnimationSmoothness", kPercentage_MIN, kPercentage_MAX,

[bruthig, 2017/03/24 14:25:39]

FYI You will need to add an entry to histograms.xml so that the UMA dashboards
surface this metric.

[wutao, 2017/03/24 20:24:37]

Done.

+        kPercentage_MAX + 1, base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(value);
+  }
+};
+
 ScreenRotationAnimator::ScreenRotationAnimator(int64_t display_id)
     : display_id_(display_id),
       is_rotating_(false),
+      metrics_reporter_(
+          base::MakeUnique<ScreenRotationAnimationMetricsReporter>()),
       disable_animation_timers_for_test_(false),
       weak_factory_(this) {}
 
@@ -278,6 +295,7 @@ void ScreenRotationAnimator::AnimateRotation(
   // control the animation.
   if (disable_animation_timers_for_test_)

[bruthig, 2017/03/24 14:25:39]

Not related to this change but shouldn't we be disabling the timer for the
|animation_sequence| above?

[wutao, 2017/03/24 20:24:37]

Ideally yes, but it will not affect the test result.
Due to that the above block animation will be replaced by the animation of
|new_layer_tree|, a screenshot after screen rotation, I would like to add the
timer flag and add the animator of the |new_layer_tree| to the testapi at that
time.

     animator->set_disable_timer_for_test(true);
+  animation_sequence->SetAnimationMetricsReporter(metrics_reporter_.get());
   animator->StartAnimation(animation_sequence.release());
 
   rotation_request.reset();