<picture>: Update the <img> element when a <source> changes

Source/core/html/HTMLImageElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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 174 matching lines @@
     if (renderer() && renderer()->isImage())
         toRenderImage(renderer())->setImageDevicePixelRatio(m_imageDevicePixelRatio);
 }
 
 void HTMLImageElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == altAttr) {
         if (renderer() && renderer()->isImage())
             toRenderImage(renderer())->updateAltText();
     } else if (name == srcAttr || name == srcsetAttr || name == sizesAttr) {
-        unsigned effectiveSize = 0;
-        if (RuntimeEnabledFeatures::pictureSizesEnabled())
-            effectiveSize = SizesAttributeParser::findEffectiveSize(fastGetAttribute(sizesAttr), MediaValuesCached::create(document()));
-        ImageCandidate candidate = bestFitSourceForImageAttributes(document().devicePixelRatio(), effectiveSize, fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr));
-        setBestFitURLAndDPRFromImageCandidate(candidate);
-        m_imageLoader.updateFromElementIgnoringPreviousError();
+        selectSourceURL(UpdateIgnorePreviousError);
     } else if (name == usemapAttr) {
         setIsLink(!value.isNull());
     } else if (name == compositeAttr) {
         // FIXME: images don't support blend modes in their compositing attribute.
         blink::WebBlendMode blendOp = blink::WebBlendModeNormal;
         if (!parseCompositeAndBlendOperator(value, m_compositeOperator, blendOp))
             m_compositeOperator = CompositeSourceOver;
     } else {
         HTMLElement::parseAttribute(name, value);
     }
@@ skipping 345 matching lines @@
     ImageResource* image = cachedImage();
     if (!image)
         return FloatSize();
     LayoutSize size;
     size = image->imageSizeForRenderer(renderer(), 1.0f); // FIXME: Not sure about this.
     if (renderer() && renderer()->isRenderImage() && image->image() && !image->image()->hasRelativeWidth())
         size.scale(toRenderImage(renderer())->imageDevicePixelRatio());
     return size;
 }
 
+void HTMLImageElement::selectSourceURL(UpdateFromElementBehavior behavior)
+{
+    bool foundURL = false;
+    if (RuntimeEnabledFeatures::pictureEnabled()) {
+        ImageCandidate candidate = findBestFitImageFromPictureParent();
+        if (!candidate.isEmpty()) {
+            setBestFitURLAndDPRFromImageCandidate(candidate);
+            foundURL = true;
+        }
+    }
+
+    if (!foundURL) {
+        unsigned effectiveSize = 0;
+        if (RuntimeEnabledFeatures::pictureSizesEnabled())
+            effectiveSize = SizesAttributeParser::findEffectiveSize(fastGetAttribute(sizesAttr), MediaValuesCached::create(document()));
+        ImageCandidate candidate = bestFitSourceForImageAttributes(document().devicePixelRatio(), effectiveSize, fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr));
+        setBestFitURLAndDPRFromImageCandidate(candidate);
+    }
+    if (behavior == UpdateIgnorePreviousError)
+        m_imageLoader.updateFromElementIgnoringPreviousError();
+    else
+        m_imageLoader.updateFromElement();
 }
+}