Use Shadow DOM to display fallback content for images

Source/core/html/HTMLImageLoader.cpp

Index: Source/core/html/HTMLImageLoader.cpp
diff --git a/Source/core/html/HTMLImageLoader.cpp b/Source/core/html/HTMLImageLoader.cpp
index 44fc879fe2f85abc3b3d5fe90ff5fef691766d39..78479403fde99240b57e72309959d41973774515 100644
--- a/Source/core/html/HTMLImageLoader.cpp
+++ b/Source/core/html/HTMLImageLoader.cpp
@@ -27,14 +27,18 @@
 #include "core/events/Event.h"
 #include "core/fetch/ImageResource.h"
 #include "core/html/HTMLImageElement.h"
+#include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLObjectElement.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "platform/Logging.h"
 
 namespace blink {
 
-HTMLImageLoader::HTMLImageLoader(Element* node)
-    : ImageLoader(node)
+using namespace HTMLNames;
+
+HTMLImageLoader::HTMLImageLoader(Element* element)
+    : ImageLoader(element)
+    , m_loadFallbackContentTimer(this, &HTMLImageLoader::timerFired)
 {
 }
 
@@ -61,17 +65,56 @@ String HTMLImageLoader::sourceURI(const AtomicString& attr) const
     return stripLeadingAndTrailingHTMLSpaces(attr);
 }
 
+static void loadFallbackContentForElement(Element* element)
+{
+    if (isHTMLImageElement(element))
+        toHTMLImageElement(element)->ensureFallbackContent();
+    else if (isHTMLInputElement(element))
+        toHTMLInputElement(element)->ensureFallbackContent();
+}
+
+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())
+        loadFallbackContentForElement(element());
+}
+
 void HTMLImageLoader::notifyFinished(Resource*)
 {
     ImageResource* cachedImage = image();
-
     RefPtrWillBeRawPtr<Element> element = this->element();
     ImageLoader::notifyFinished(cachedImage);
 
     bool loadError = cachedImage->errorOccurred() || cachedImage->response().httpStatusCode() >= 400;
+    if (isHTMLImageElement(*element)) {
+        if (loadError)
+            ensureFallbackContent();
+        else
+            toHTMLImageElement(element)->ensurePrimaryContent();
+    }
+
+    if (isHTMLInputElement(*element)) {
+        if (loadError)
+            ensureFallbackContent();
+        else
+            toHTMLInputElement(element)->ensurePrimaryContent();
+    }
 
     if (loadError && isHTMLObjectElement(*element))
         toHTMLObjectElement(element)->renderFallbackContent();
 }
 
+void HTMLImageLoader::ensureFallbackContent()
+{
+    if (image()->url().protocolIsData())
+        m_loadFallbackContentTimer.startOneShot(0, FROM_HERE);
+    else
+        loadFallbackContentForElement(element());
+}
+
+void HTMLImageLoader::timerFired(Timer<HTMLImageLoader>*)
+{
+    loadFallbackContentForElement(element());
+}
 }