Use Shadow DOM to display fallback content for images

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 3773 matching lines @@
     if (isInline() || !avoidsFloats() || isFloating())
         return false;
 
     // Only auto width objects can possibly shrink to avoid floats.
     return style()->width().isAuto();
 }
 
 static bool isReplacedElement(Node* node)
 {
     // Checkboxes and radioboxes are not isReplaced() nor do they have their own renderer in which to override avoidFloats().
-    return node && node->isElementNode() && toElement(node)->isFormControlElement();
+    return node && node->isElementNode() && (toElement(node)->isFormControlElement() || isHTMLImageElement(toElement(node)));
 }
 
 bool RenderBox::avoidsFloats() const
 {
     return isReplaced() || isReplacedElement(node()) || hasOverflowClip() || isHR() || isLegend() || isWritingModeRoot() || isFlexItemIncludingDeprecated();
 }
 
 bool RenderBox::hasNonCompositedScrollbars() const
 {
     if (RenderLayer* layer = this->layer()) {
@@ skipping 679 matching lines @@
     computedValues.m_margins.m_end = marginEnd();
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setLogicalLeft(oldLogicalLeft);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 }
 
 } // namespace blink