Use Shadow DOM to display fallback content for images

Source/core/html/HTMLImageLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "config.h"
 #include "core/html/HTMLImageLoader.h"
 
 #include "core/HTMLNames.h"
 #include "core/dom/Element.h"
+#include "core/dom/Microtask.h"
 #include "core/events/Event.h"
 #include "core/fetch/ImageResource.h"
-#include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLObjectElement.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "platform/Logging.h"
+#include "public/platform/WebThread.h"
 
 namespace blink {
 
+using namespace HTMLNames;
+
+class HTMLImageLoader::EnsureFallbackContentTask : public blink::WebThread::Task {

[pdr., 2014/11/14 07:34:17]

A Timer with startOneShot seems like it would be much simpler.

+public:
+    static PassOwnPtr<EnsureFallbackContentTask> create(HTMLElement* element)
+    {
+        return adoptPtr(new EnsureFallbackContentTask(element));
+    }
+
+    EnsureFallbackContentTask(HTMLElement* element)
+        : m_element(element)
+    {
+    }
+    virtual void run() override

[pdr., 2014/11/14 07:34:17]

Nit: missing newline.

+    {
+        m_element->ensureFallbackContent();
+    }
+
+private:
+    HTMLElement* m_element;
+};
+
 HTMLImageLoader::HTMLImageLoader(Element* node)
     : ImageLoader(node)
 {
 }
 
 HTMLImageLoader::~HTMLImageLoader()
 {
 }
 
 void HTMLImageLoader::dispatchLoadEvent()
 {
     WTF_LOG(Timers, "HTMLImageLoader::dispatchLoadEvent %p", this);
 
     // HTMLVideoElement uses this class to load the poster image, but it should not fire events for loading or failure.
     if (isHTMLVideoElement(*element()))
         return;
 
     bool errorOccurred = image()->errorOccurred();
     if (isHTMLObjectElement(*element()) && !errorOccurred)
         errorOccurred = (image()->response().httpStatusCode() >= 400); // An <object> considers a 404 to be an error and should fire onerror.
     element()->dispatchEvent(Event::create(errorOccurred ? EventTypeNames::error : EventTypeNames::load));
 }
 
 String HTMLImageLoader::sourceURI(const AtomicString& attr) const
 {
     return stripLeadingAndTrailingHTMLSpaces(attr);
 }
 
+void HTMLImageLoader::noImageResourceToLoad()
+{
+    // FIXME: Use fallback content even when there is no alt-text. The only blocker is the large amount of rebaselining it requires.
+    if (!toHTMLElement(element())->altText().isEmpty())
+        toHTMLElement(element())->ensureFallbackContent();
+}
+
 void HTMLImageLoader::notifyFinished(Resource*)
 {
     ImageResource* cachedImage = image();
 
-    RefPtrWillBeRawPtr<Element> element = this->element();
     ImageLoader::notifyFinished(cachedImage);
 
     bool loadError = cachedImage->errorOccurred() || cachedImage->response().httpStatusCode() >= 400;
+    if (loadError)
+        ensureFallbackContent();
+    else
+        toHTMLElement(element())->ensurePrimaryContent();
 
-    if (loadError && isHTMLObjectElement(*element))
-        toHTMLObjectElement(element)->renderFallbackContent();
+    if (loadError && isHTMLObjectElement(element()))
+        toHTMLObjectElement(element())->renderFallbackContent();
 }
 
+void HTMLImageLoader::ensureFallbackContent()
+{
+    if (image()->url().protocolIsData()) {
+        OwnPtr<EnsureFallbackContentTask> task = EnsureFallbackContentTask::create(toHTMLElement(element()));
+        Microtask::enqueueMicrotask(task.release());
+    } else {
+        toHTMLElement(element())->ensureFallbackContent();
+    }
 }
+}