Use Shadow DOM to display fallback content for images

Source/modules/accessibility/AXRenderObject.cpp

 /*
 * Copyright (C) 2008 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
@@ skipping 235 matching lines @@
     if (!m_renderer || !m_renderer->isBox())
         return 0;
 
     RenderBox* box = toRenderBox(m_renderer);
     if (!box->canBeScrolledAndHasScrollableArea())
         return 0;
 
     return box->scrollableArea();
 }
 
+static bool isImageOrAltText(RenderBoxModelObject* box, Node* node)
+{
+    if (box && box->isImage())
+        return true;
+    if (isHTMLImageElement(node))
+        return true;
+    if (isHTMLInputElement(node) && toHTMLInputElement(node)->hasFallbackContent())
+        return true;
+    return false;
+}
+
 AccessibilityRole AXRenderObject::determineAccessibilityRole()
 {
     if (!m_renderer)
         return UnknownRole;
 
     if ((m_ariaRole = determineAriaRoleAttribute()) != UnknownRole)
         return m_ariaRole;
 
     Node* node = m_renderer->node();
     RenderBoxModelObject* cssBox = renderBoxModelObject();
 
     if ((cssBox && cssBox->isListItem()) || isHTMLLIElement(node))
         return ListItemRole;
     if (m_renderer->isListMarker())
         return ListMarkerRole;
     if (isHTMLLegendElement(node))
         return LegendRole;
     if (m_renderer->isText())
         return StaticTextRole;
-    if (cssBox && cssBox->isImage()) {
+    if (cssBox && isImageOrAltText(cssBox, node)) {
         if (node && node->isLink())
             return ImageMapRole;
         if (isHTMLInputElement(node))
             return ariaHasPopup() ? PopUpButtonRole : ButtonRole;
         if (isSVGImage())
             return SVGRootRole;
         return ImageRole;
     }
     // Note: if JavaScript is disabled, the renderer won't be a RenderHTMLCanvas.
     if (isHTMLCanvasElement(node) && m_renderer->isCanvas())
@@ skipping 390 matching lines @@
             Element* elt = toElement(node);
             const AtomicString& alt = elt->getAttribute(altAttr);
             // don't ignore an image that has an alt tag
             if (!alt.string().containsOnlyWhitespace())
                 return false;
             // informal standard is to ignore images with zero-length alt strings
             if (!alt.isNull())
                 return true;
         }
 
-        if (isNativeImage() && m_renderer->isImage()) {
+        if (isNativeImage() && isImageOrAltText(toRenderBoxModelObject(m_renderer), node)) {
             // check for one-dimensional image
             RenderImage* image = toRenderImage(m_renderer);
             if (image->size().height() <= 1 || image->size().width() <= 1)
                 return true;
 
             // check whether rendered image was stretched from one-dimensional file image
             if (image->cachedImage()) {
                 LayoutSize imageSize = image->cachedImage()->imageSizeForRenderer(m_renderer, image->view()->zoomFactor());
                 return imageSize.height() <= 1 || imageSize.width() <= 1;
             }
@@ skipping 1700 matching lines @@
         if (label && label->renderer()) {
             LayoutRect labelRect = axObjectCache()->getOrCreate(label)->elementRect();
             result.unite(labelRect);
         }
     }
 
     return result;
 }
 
 } // namespace blink