Implement <video controls> dodging for text track layout

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index 06cb425ff88e530813761940ec6ea550653efed8..6749d07d3465b3053d65296d1043b9749a3befe8 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -236,6 +236,10 @@ public:
     // Note that this can be non-null even if there is no controls attribute.
     MediaControls* mediaControls() const;
 
+    // Notifies the media element that the media controls became visible, so
+    // that text track layout may be updated to avoid overlapping them.
+    void mediaControlsDidBecomeVisible();
+
     void sourceWasRemoved(HTMLSourceElement*);
     void sourceWasAdded(HTMLSourceElement*);