[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..8109ad1524bfe4a707bcd9d9da08383f704177d6 100644
--- a/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
+++ b/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
@@ -852,6 +852,10 @@ void MediaControls::onPlay() {
   startHideMediaControlsTimer();
 }
 
+void MediaControls::onPlaying() {
+  m_timeline->onPlaying();
+}
+
 void MediaControls::onPause() {
   updatePlayState();
   m_timeline->setPosition(mediaElement().currentTime());