Use Shadow DOM to display fallback content for images

Source/core/loader/ImageLoader.cpp

Index: Source/core/loader/ImageLoader.cpp
diff --git a/Source/core/loader/ImageLoader.cpp b/Source/core/loader/ImageLoader.cpp
index 18e1b17652f88462f426e2960891bc1d4075a005..f9ffd4c1efc167515f9ec3887ce9427738b4b261 100644
--- a/Source/core/loader/ImageLoader.cpp
+++ b/Source/core/loader/ImageLoader.cpp
@@ -267,8 +267,11 @@ void ImageLoader::doUpdateFromElement(BypassMainWorldBehavior bypassBehavior, Up
         // Fire an error event if the url string is not empty, but the KURL is.
         m_hasPendingErrorEvent = true;
         errorEventSender().dispatchEventSoon(this);
+    } else {
+        noImageResourceToLoad();
     }
 
+
     ImageResource* oldImage = m_image.get();
     if (newImage != oldImage) {
         sourceImageChanged();
@@ -329,7 +332,7 @@ void ImageLoader::updateFromElement(UpdateFromElementBehavior updateBehavior, Lo
     }
 
     KURL url = imageSourceToKURL(imageSourceURL);
-    if (imageSourceURL.isNull() || url.isNull() || shouldLoadImmediately(url, loadType)) {
+    if ((!imageSourceURL.isNull() && url.isNull()) || shouldLoadImmediately(url, loadType)) {

[esprehn, 2014/09/05 00:47:52]

Why did you change this?

[rhogan, 2014/09/08 19:52:42]

This allows images with no src="" to go through the image loading process. When
they error out we can invoke the fallback content.

         doUpdateFromElement(DoNotBypassMainWorldCSP, updateBehavior);
         return;
     }
@@ -359,7 +362,8 @@ bool ImageLoader::shouldLoadImmediately(const KURL& url, LoadType loadType) cons
         || isHTMLObjectElement(m_element)
         || isHTMLEmbedElement(m_element)
         || url.protocolIsData()
-        || memoryCache()->resourceForURL(url)
+        || !element()->document().frame()

[esprehn, 2014/09/05 00:47:52]

What are you checking here? I think you mean document().isActive() ?

[rhogan, 2014/09/08 19:52:43]

When creating the MicroTask there's an
ASSERT(loader->element()->document().frame()); in shouldBypassMainWorldCSP().

+        || (!url.isNull() && memoryCache()->resourceForURL(url))
         || loadType == ForceLoadImmediately);
 }