Use Shadow DOM to display fallback content for images

Source/core/fetch/ImageResource.h

Index: Source/core/fetch/ImageResource.h
diff --git a/Source/core/fetch/ImageResource.h b/Source/core/fetch/ImageResource.h
index 72184dfa9b3776ce04e637a7a69acd6f108aef6f..bf5e6791f7a2eeac3e78832a95f510761263a743 100644
--- a/Source/core/fetch/ImageResource.h
+++ b/Source/core/fetch/ImageResource.h
@@ -60,9 +60,6 @@ public:
     bool hasImage() const { return m_image.get(); }
     bool currentFrameKnownToBeOpaque(const RenderObject*); // Side effect: ensures decoded image is in cache, therefore should only be called when about to draw the image.
 
-    static std::pair<blink::Image*, float> brokenImage(float deviceScaleFactor); // Returns an image and the image's resolution scale factor.
-    bool willPaintBrokenImage() const;
-
     bool canRender(const RenderObject& renderer, float multiplier) { return !errorOccurred() && !imageSizeForRenderer(&renderer, multiplier).isEmpty(); }
 
     void setContainerSizeForRenderer(const ImageResourceClient*, const IntSize&, float);