Revert of RenderFlexibleBox should be treated as a candidate for visible position.

Source/core/dom/Position.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2009 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 873 matching lines @@
         // associated renderer returns isText() true, e.g. LayoutSVGInlineText.
         return false;
     }
 
     if (isRenderedHTMLTableElement(deprecatedNode()) || editingIgnoresContent(deprecatedNode()))
         return (atFirstEditingPositionForNode() || atLastEditingPositionForNode()) && !nodeIsUserSelectNone(deprecatedNode()->parentNode());
 
     if (isHTMLHtmlElement(*m_anchorNode))
         return false;
 
-    if (renderer->isLayoutBlockFlow() || renderer->isFlexibleBox() || renderer->isLayoutGrid()) {
+    if (renderer->isLayoutBlockFlow() || renderer->isLayoutGrid()) {
         if (toLayoutBlock(renderer)->logicalHeight() || isHTMLBodyElement(*m_anchorNode)) {
             if (!Position::hasRenderedNonAnonymousDescendantsWithHeight(renderer))
                 return atFirstEditingPositionForNode() && !Position::nodeIsUserSelectNone(deprecatedNode());
             return m_anchorNode->hasEditableStyle() && !Position::nodeIsUserSelectNone(deprecatedNode()) && atEditingBoundary();
         }
     } else {
         LocalFrame* frame = m_anchorNode->document().frame();
         bool caretBrowsing = frame->settings() && frame->settings()->caretBrowsingEnabled();
         return (caretBrowsing || m_anchorNode->hasEditableStyle()) && !Position::nodeIsUserSelectNone(deprecatedNode()) && atEditingBoundary();
     }
@@ skipping 461 matching lines @@
     pos.showTreeForThis();
 }
 
 void showTree(const blink::Position* pos)
 {
     if (pos)
         pos->showTreeForThis();
 }
 
 #endif