Implement heuristic for showing media controls during playback w/o a mouse

Source/core/html/shadow/MediaControls.h

Index: Source/core/html/shadow/MediaControls.h
diff --git a/Source/core/html/shadow/MediaControls.h b/Source/core/html/shadow/MediaControls.h
index 6379f7a2eb25699989fd721f32f572a0397ddfb0..a978c6ab1aa56f87302999051f1405829c36cd37 100644
--- a/Source/core/html/shadow/MediaControls.h
+++ b/Source/core/html/shadow/MediaControls.h
@@ -66,6 +66,8 @@ public:
 
     void updateTextTrackDisplay();
 
+    void mediaElementFocused();
+
 private:
     explicit MediaControls(HTMLMediaElement&);
 
@@ -77,6 +79,7 @@ private:
     void updatePlayState();
 
     bool shouldHideMediaControls();
+    bool shouldShowMediaControls() const;
     void hideMediaControlsTimerFired(Timer<MediaControls>*);
     void startHideMediaControlsTimer();
     void stopHideMediaControlsTimer();