Separate VTTCue from VTTCueBox and LayoutVTTCue

Source/core/layout/LayoutVTTCue.h

 /*
  * Copyright (C) 2012 Victor Carbune (victor@rosedu.org)
  *
  * 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 13 matching lines @@
  */
 
 #ifndef LayoutVTTCue_h
 #define LayoutVTTCue_h
 
 #include "core/layout/LayoutBlockFlow.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
-class VTTCue;
 class VTTCueBox;
 
 class LayoutVTTCue final : public LayoutBlockFlow {
 public:
-    explicit LayoutVTTCue(VTTCueBox*);
+    LayoutVTTCue(ContainerNode*, float snapToLinesPosition);
+
+    // The computed line position for snap-to-lines layout, and NaN for
+    // non-snap-to-lines layout where no adjustment should take place.
+    float snapToLinesPosition() { return m_snapToLinesPosition; }
 
 private:
     void layout() override;
 
     void adjustForTopAndBottomMarginBorderAndPadding();
     void repositionCueSnapToLinesNotSet();
 
-    // VTTCue is kept alive by VTTCueBox.
-    GC_PLUGIN_IGNORE("http://crbug.com/509911")
-    VTTCue* m_cue;
+    float m_snapToLinesPosition;
 };
 
 } // namespace blink
 
 #endif // LayoutVTTCue_h