WebVTT: Support 'auto' text position

Source/core/html/track/vtt/VTTCue.h

 /*
  * Copyright (c) 2013, Opera Software ASA. 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 62 matching lines @@
 
     const String& vertical() const;
     void setVertical(const String&);
 
     bool snapToLines() const { return m_snapToLines; }
     void setSnapToLines(bool);
 
     void line(DoubleOrAutoKeyword&) const;
     void setLine(const DoubleOrAutoKeyword&, ExceptionState&);
 
-    double position() const { return m_textPosition; }
-    void setPosition(double, ExceptionState&);
+    void position(DoubleOrAutoKeyword&) const;
+    void setPosition(const DoubleOrAutoKeyword&, ExceptionState&);
 
     double size() const { return m_cueSize; }
     void setSize(double, ExceptionState&);
 
     const String& align() const;
     void setAlign(const String&);
 
     const String& text() const { return m_text; }
     void setText(const String&);
 
@@ skipping 58 matching lines @@
 
     virtual void cueDidChange() override;
 
     void createVTTNodeTree();
     void copyVTTNodeToDOMTree(ContainerNode* vttNode, ContainerNode* root);
 
     FloatPoint getPositionCoordinates() const;
     bool lineIsAuto() const;
 
     void calculateDisplayParameters();
+    float calculateComputedTextPosition() const;
+    bool textPositionIsAuto() const;
 
     enum CueSetting {
         None,
         Vertical,
         Line,
         Position,
         Size,
         Align,
         RegionId
     };
@@ skipping 20 matching lines @@
     bool m_displayTreeShouldChange : 1;
     bool m_notifyRegion : 1;
 };
 
 // VTTCue is currently the only TextTrackCue subclass.
 DEFINE_TYPE_CASTS(VTTCue, TextTrackCue, cue, true, true);
 
 } // namespace blink
 
 #endif // VTTCue_h