Use Shadow DOM to display fallback content for images

Source/core/loader/ImageLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 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.
  *
@@ skipping 48 matching lines @@
 
 static inline bool pageIsBeingDismissed(Document* document)
 {
     return document->pageDismissalEventBeingDispatched() != Document::NoDismissal;
 }
 
 static ImageLoader::BypassMainWorldBehavior shouldBypassMainWorldCSP(ImageLoader* loader)
 {
     ASSERT(loader);
     ASSERT(loader->element());
-    ASSERT(loader->element()->document().frame());
-    if (loader->element()->document().frame()->script().shouldBypassMainWorldCSP())
+    if (loader->element()->document().frame() && loader->element()->document().frame()->script().shouldBypassMainWorldCSP())
         return ImageLoader::BypassMainWorldCSP;
     return ImageLoader::DoNotBypassMainWorldCSP;
 }
 
 class ImageLoader::Task : public blink::WebThread::Task {
 public:
     static PassOwnPtr<Task> create(ImageLoader* loader, UpdateFromElementBehavior updateBehavior)
     {
         return adoptPtr(new Task(loader, updateBehavior));
     }
@@ skipping 180 matching lines @@
 
         if (m_loadingImageDocument)
             newImage = createImageResourceForImageDocument(document, request);
         else
             newImage = document.fetcher()->fetchImage(request);
 
         if (!newImage && !pageIsBeingDismissed(&document))
             crossSiteOrCSPViolationOccured(imageSourceURL);
         else
             clearFailedLoadURL();
-    } else if (!imageSourceURL.isNull()) {
-        // Fire an error event if the url string is not empty, but the KURL is.
-        m_hasPendingErrorEvent = true;
-        errorEventSender().dispatchEventSoon(this);
+    } else {
+        if (!imageSourceURL.isNull()) {
+            // Fire an error event if the url string is not empty, but the KURL is.
+            m_hasPendingErrorEvent = true;
+            errorEventSender().dispatchEventSoon(this);
+        }
+        noImageResourceToLoad();
     }
 
     ImageResource* oldImage = m_image.get();
     if (newImage != oldImage) {
         sourceImageChanged();
 
         if (m_hasPendingLoadEvent) {
             loadEventSender().cancelEvent(this);
             m_hasPendingLoadEvent = false;
         }
@@ skipping 24 matching lines @@
     }
 
     if (RenderImageResource* imageResource = renderImageResource())
         imageResource->resetAnimation();
 
     // Only consider updating the protection ref-count of the Element immediately before returning
     // from this function as doing so might result in the destruction of this ImageLoader.
     updatedHasPendingEvent();
 }
 
-void ImageLoader::updateFromElement(UpdateFromElementBehavior updateBehavior, LoadType loadType)
+void ImageLoader::updateFromElement(UpdateFromElementBehavior updateBehavior)
 {
     AtomicString imageSourceURL = m_element->imageSourceURL();
 
     if (updateBehavior == UpdateIgnorePreviousError)
         clearFailedLoadURL();
 
     if (!m_failedLoadURL.isEmpty() && imageSourceURL == m_failedLoadURL)
         return;
 
     // If we have a pending task, we have to clear it -- either we're
     // now loading immediately, or we need to reset the task's state.
     if (m_pendingTask) {
         m_pendingTask->clearLoader();
         m_pendingTask.clear();
     }
 
     KURL url = imageSourceToKURL(imageSourceURL);
-    if (imageSourceURL.isNull() || url.isNull() || shouldLoadImmediately(url, loadType)) {
+    if (shouldLoadImmediately(url)) {
         doUpdateFromElement(DoNotBypassMainWorldCSP, updateBehavior);
         return;
     }
     enqueueImageLoadingMicroTask(updateBehavior);
 }
 
 KURL ImageLoader::imageSourceToKURL(AtomicString imageSourceURL) const
 {
     KURL url;
 
     // Don't load images for inactive documents. We don't want to slow down the
     // raw HTML parsing case by loading images we don't intend to display.
     Document& document = m_element->document();
     if (!document.isActive())
         return url;
 
     // Do not load any image if the 'src' attribute is missing or if it is
     // an empty string.
     if (!imageSourceURL.isNull() && !stripLeadingAndTrailingHTMLSpaces(imageSourceURL).isEmpty())
         url = document.completeURL(sourceURI(imageSourceURL));
     return url;
 }
 
-bool ImageLoader::shouldLoadImmediately(const KURL& url, LoadType loadType) const
+bool ImageLoader::shouldLoadImmediately(const KURL& url) const
 {
+    // We force failed image loads through the asynchronous path so that we can add the shadow DOM
+    // for the alt-text content when style recalc is over and DOM mutation is allowed again.
+    if (!url.isNull()) {
+        Resource* resource = memoryCache()->resourceForURL(url);
+        if (resource && !resource->errorOccurred())
+            return true;
+    }
     return (m_loadingImageDocument
         || isHTMLObjectElement(m_element)
         || isHTMLEmbedElement(m_element)
-        || url.protocolIsData()
-        || memoryCache()->resourceForURL(url)
-        || loadType == ForceLoadImmediately);
+        || url.protocolIsData());
 }
 
 void ImageLoader::notifyFinished(Resource* resource)
 {
     WTF_LOG(Timers, "ImageLoader::notifyFinished %p; m_hasPendingLoadEvent=%d",
         this, m_hasPendingLoadEvent);
 
     ASSERT(m_failedLoadURL.isEmpty());
     ASSERT(resource == m_image.get());
 
@@ skipping 192 matching lines @@
 }
 
 #if ENABLE(OILPAN)
 ImageLoader::ImageLoaderClientRemover::~ImageLoaderClientRemover()
 {
     m_loader.willRemoveClient(m_client);
 }
 #endif
 
 }