[Media Controls] Add UMA for timeline scrubber

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

Index: third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
diff --git a/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp b/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
index 6fcf2642e672bbb9fa145f243b43bcf7045fa993..ee06e67b169c75f739f3c041dec6a96c2ce1d66d 100644
--- a/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
+++ b/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
@@ -205,6 +205,7 @@ MediaControls::MediaControls(HTMLMediaElement& mediaElement)
       m_hideTimerBehaviorFlags(IgnoreNone),
       m_isMouseOverControls(false),
       m_isPausedForScrubbing(false),
+      m_hasNeverBeenPlayed(true),
       m_resizeObserver(ResizeObserver::create(
           mediaElement.document(),
           new MediaControlsResizeObserverCallback(this))),
@@ -845,6 +846,11 @@ void MediaControls::onDurationChange() {
 }
 
 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();