Make FrameCaret contains CaretBase instead of deriving from it

third_party/WebKit/Source/core/editing/DragCaretController.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 86 matching lines @@
   if (!anchorNode)
     return;
   if (!node.isShadowIncludingInclusiveAncestorOf(anchorNode))
     return;
   m_position.document()->layoutViewItem().clearSelection();
   clear();
 }
 
 DEFINE_TRACE(DragCaretController) {
   visitor->trace(m_position);
-  visitor->trace(m_caretBase);
   SynchronousMutationObserver::trace(visitor);
 }
 
 void DragCaretController::paintDragCaret(LocalFrame* frame,
                                          GraphicsContext& context,
                                          const LayoutPoint& paintOffset) const {
   if (m_position.anchorNode()->document().frame() == frame) {
     CaretBase::paintCaret(m_position.anchorNode(), context, *m_caretBase,
                           m_caretLocalRect, paintOffset,
                           DisplayItem::kDragCaret);
   }
 }
 
 }  // namespace blink