[Media Controls] Add UMA for timeline scrubber

third_party/WebKit/Source/core/html/shadow/MediaControlTimelineMetrics.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MediaControlTimelineMetrics_h
+#define MediaControlTimelineMetrics_h
+
+#include "platform/Histogram.h"
+#include "platform/wtf/Time.h"
+
+namespace blink {
+
+// Helpers for tracking and reporting media control timeline metrics to UMA.
+class MediaControlTimelineMetrics {
+ public:
+  // Start tracking a pointer gesture. |fromThumb| indicates whether the user
+  // started dragging from the thumb, as opposed to pressing down their pointer
+  // on some other part of the timeline track (causing time to jump).
+  void startGesture(bool fromThumb);
+  // Finish tracking and report a pointer gesture.
+  void recordEndGesture(int timelineWidth, double mediaDurationSeconds);
+
+  // Start tracking a keydown. Ok to call multiple times if key repeats.
+  void startKey();
+  // Finish tracking and report a keyup. Call only once even if key repeats.
+  void recordEndKey(int timelineWidth, int keyCode);
+
+  // Track an incremental input event caused by the current pointer gesture or
+  // pressed key. Each sequence of calls to this should usually be sandwiched by
+  // startGesture/Key and recordEndGesture/Key.
+  void onInput(double fromSeconds, double toSeconds);
+
+  // Report width to UMA. Should be called the first time the media is played.
+  void recordWidthOnFirstPlay(bool isFullscreen,
+                              bool isPortrait,
+                              int timelineWidth);
+
+ private:
+  enum class State {
+    // No active gesture. Progresses to kKeyDown on |startKey|, or
+    // kGestureFromThumb/kGestureFromElsewhere on |startGesture|.
+    kInactive,

[mlamouri (slow - plz ping), 2017/03/30 21:43:00]

nit: drop the k? :)

[johnme, 2017/03/31 13:47:23]

https://sites.google.com/a/chromium.org/dev/blink/coding-style
[names-enum-members] says kInterCaps is preferable for new code. Though perhaps
that advice predates enum classes, where the State:: prefix already makes it
clear that it's an enum value?

+
+    // Pointer down on thumb. Progresses to kDragFromThumb in |onInput|.
+    kGestureFromThumb,
+    // Thumb is being dragged (drag started from thumb).
+    kDragFromThumb,
+
+    // Pointer down on track. Progresses to kClick in |onInput|.
+    kGestureFromElsewhere,
+    // Pointer down followed by input. Assumed to be a click, unless additional
+    // |onInput| are received - if so progresses to kDragFromElsewhere.
+    kClick,
+    // Thumb is being dragged (drag started from track).
+    kDragFromElsewhere,
+
+    // A key is currently pressed down.
+    kKeyDown
+  };
+
+  State m_state = State::kInactive;
+
+  // The following are only valid during a pointer gesture.
+  TimeTicks m_dragStartTimeTicks;
+  float m_dragDeltaMediaSeconds = 0;
+  float m_dragSumAbsDeltaMediaSeconds = 0;
+};
+
+}  // namespace blink
+
+#endif  // MediaControlTimelineMetrics_h