Use Shadow DOM to display fallback content for images

Source/core/loader/ImageLoader.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2009 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 45 matching lines @@
 
 template<typename T> class EventSender;
 typedef EventSender<ImageLoader> ImageEventSender;
 
 class ImageLoader : public NoBaseWillBeGarbageCollectedFinalized<ImageLoader>, public ImageResourceClient {
 public:
     explicit ImageLoader(Element*);
     virtual ~ImageLoader();
     void trace(Visitor*);
 
-    enum LoadType {
-        LoadNormally,
-        ForceLoadImmediately
-    };
-
     enum UpdateFromElementBehavior {
         // This should be the update behavior when the element is attached to a document, or when DOM mutations trigger a new load.
         // Starts loading if a load hasn't already been started.
         UpdateNormal,
         // This should be the update behavior when the resource was changed (via 'src', 'srcset' or 'sizes').
         // Starts a new load even if a previous load of the same resource have failed, to match Firefox's behavior.
         // FIXME - Verify that this is the right behavior according to the spec.
         UpdateIgnorePreviousError,
         // This forces the image to update its intrinsic size, even if the image source has not changed.
         UpdateSizeChanged
     };
 
     enum BypassMainWorldBehavior {
         BypassMainWorldCSP,
         DoNotBypassMainWorldCSP
     };
 
-    void updateFromElement(UpdateFromElementBehavior = UpdateNormal, LoadType = LoadNormally);
+    void updateFromElement(UpdateFromElementBehavior = UpdateNormal);
 
     void elementDidMoveToNewDocument();
 
     Element* element() const { return m_element; }
     bool imageComplete() const
     {
         return m_imageComplete && !m_pendingTask;
     }
 
     ImageResource* image() const { return m_image.get(); }
     void setImage(ImageResource*); // Cancels pending load events, and doesn't dispatch new ones.
 
     void setLoadingImageDocument() { m_loadingImageDocument = true; }
 
     bool hasPendingActivity() const
     {
         return m_hasPendingLoadEvent || m_hasPendingErrorEvent || m_pendingTask;
     }
 
     void dispatchPendingEvent(ImageEventSender*);
 
     static void dispatchPendingLoadEvents();
     static void dispatchPendingErrorEvents();
 
     void addClient(ImageLoaderClient*);
     void removeClient(ImageLoaderClient*);
-
 protected:
     virtual void notifyFinished(Resource*) override;
 
 private:
     class Task;
 
     // Called from the task or from updateFromElement to initiate the load.
     void doUpdateFromElement(BypassMainWorldBehavior, UpdateFromElementBehavior);
 
     virtual void dispatchLoadEvent() = 0;
     virtual String sourceURI(const AtomicString&) const = 0;
+    virtual void noImageResourceToLoad() { };
 
     void updatedHasPendingEvent();
 
     void dispatchPendingLoadEvent();
     void dispatchPendingErrorEvent();
 
     RenderImageResource* renderImageResource();
     void updateRenderer();
 
     void setImageWithoutConsideringPendingLoadEvent(ImageResource*);
     void sourceImageChanged();
     void clearFailedLoadURL();
     void dispatchErrorEvent();
     void crossSiteOrCSPViolationOccurred(AtomicString);
     void enqueueImageLoadingMicroTask(UpdateFromElementBehavior);
     static ResourcePtr<ImageResource> createImageResourceForImageDocument(Document&, FetchRequest&);
 
     void timerFired(Timer<ImageLoader>*);
 
     KURL imageSourceToKURL(AtomicString) const;
 
     // Used to determine whether to immediately initiate the load
     // or to schedule a microtask.
-    bool shouldLoadImmediately(const KURL&, LoadType) const;
+    bool shouldLoadImmediately(const KURL&) const;
 
     void willRemoveClient(ImageLoaderClient&);
 
     RawPtrWillBeMember<Element> m_element;
     ResourcePtr<ImageResource> m_image;
     // FIXME: Oilpan: We might be able to remove this Persistent hack when
     // ImageResourceClient is traceable.
     GC_PLUGIN_IGNORE("http://crbug.com/383741")
     RefPtrWillBePersistent<Element> m_keepAlive;
 #if ENABLE(OILPAN)
@@ skipping 26 matching lines @@
     bool m_imageComplete : 1;
     bool m_loadingImageDocument : 1;
     bool m_elementIsProtected : 1;
     bool m_suppressErrorEvents : 1;
     unsigned m_highPriorityClientCount;
 };
 
 }
 
 #endif