[Media Controls] Add UMA for timeline scrubber

third_party/WebKit/Source/core/html/shadow/MediaControls.cpp

 /*
  * Copyright (C) 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 187 matching lines @@
           this,
           WTF::bind(&MediaControls::hideAllMenus, wrapWeakPersistent(this)))),
       m_orientationLockDelegate(nullptr),
       m_hideMediaControlsTimer(TaskRunnerHelper::get(TaskType::UnspecedTimer,
                                                      &mediaElement.document()),
                                this,
                                &MediaControls::hideMediaControlsTimerFired),
       m_hideTimerBehaviorFlags(IgnoreNone),
       m_isMouseOverControls(false),
       m_isPausedForScrubbing(false),
+      m_hasNeverBeenPlayed(true),
       m_resizeObserver(ResizeObserver::create(
           mediaElement.document(),
           new MediaControlsResizeObserverCallback(this))),
       m_elementSizeChangedTimer(TaskRunnerHelper::get(TaskType::UnspecedTimer,
                                                       &mediaElement.document()),
                                 this,
                                 &MediaControls::elementSizeChangedTimerFired),
       m_keepShowingUntilTimerFires(false) {
   m_resizeObserver->observe(m_mediaElement);
 }
@@ skipping 620 matching lines @@
   m_durationDisplay->setTextContent(
       LayoutTheme::theme().formatMediaControlsTime(duration));
   m_durationDisplay->setCurrentValue(duration);
   updateCurrentTimeDisplay();
 
   // Update the timeline (the UI with the seek marker).
   m_timeline->setDuration(duration);
 }
 
 void MediaControls::onPlay() {
+  if (m_hasNeverBeenPlayed) {
+    m_timeline->recordWidthOnFirstPlay();
+    m_hasNeverBeenPlayed = false;
+  }

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

Would it make sense to have this in onLoadedMetadata instead?
MediaContorlTimelineMetrics could keep track of whether it was recorded already?

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

Moved to a new onPlayed event as discussed.
Done.

+
   updatePlayState();
   m_timeline->setPosition(mediaElement().currentTime());
   updateCurrentTimeDisplay();
 
   startHideMediaControlsTimer();
 }
 
 void MediaControls::onPause() {
   updatePlayState();
   m_timeline->setPosition(mediaElement().currentTime());
@@ skipping 242 matching lines @@
   visitor->trace(m_overflowList);
   visitor->trace(m_castButton);
   visitor->trace(m_overlayCastButton);
   visitor->trace(m_mediaEventListener);
   visitor->trace(m_windowEventListener);
   visitor->trace(m_orientationLockDelegate);
   HTMLDivElement::trace(visitor);
 }
 
 }  // namespace blink