Handle AX help-Text for media time slider.

Source/modules/accessibility/AXNodeObject.h

 /*
  * Copyright (C) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 73 matching lines @@
     //
 
     virtual void init() override;
     virtual void detach() override;
     virtual bool isDetached() const override { return !m_node; }
     virtual bool isAXNodeObject() const override final { return true; }
 
     // Check object role or purpose.
     virtual bool isAnchor() const override final;
     virtual bool isControl() const override;
+    bool isControllingVideoElement() const;
     virtual bool isEmbeddedObject() const override final;
     virtual bool isFieldset() const override final;
     virtual bool isHeading() const override final;
     virtual bool isHovered() const override final;
     virtual bool isImage() const override final;
     bool isImageButton() const;
     virtual bool isInputImage() const override final;
     virtual bool isLink() const override final;
     virtual bool isMenu() const override final;
     virtual bool isMenuButton() const override final;
@@ skipping 91 matching lines @@
     void changeValueByPercent(float percentChange);
     float stepValueForRange() const;
     AXObject* findChildWithTagName(const HTMLQualifiedName&) const;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXNodeObject, isAXNodeObject());
 
 } // namespace blink
 
 #endif // AXNodeObject_h