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

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index 4347402073a7f384e9471d309754eb50903834ab..ca7dd4abd22af3e259ba8718e6113cbac5692800 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -3630,6 +3630,15 @@ bool HTMLMediaElement::isInteractiveContent() const
     return fastHasAttribute(controlsAttr);
 }
 
+void HTMLMediaElement::defaultEventHandler(Event* event)
+{
+    if (event->type() == EventTypeNames::focusin) {
+        if (hasMediaControls())
+            mediaControls()->mediaElementFocused();
+    }
+    HTMLElement::defaultEventHandler(event);
+}
+
 void HTMLMediaElement::trace(Visitor* visitor)
 {
     visitor->trace(m_error);