Have srcset respond to viewport changes

Source/core/html/HTMLImageElement.h

Index: Source/core/html/HTMLImageElement.h
diff --git a/Source/core/html/HTMLImageElement.h b/Source/core/html/HTMLImageElement.h
index 4d1f09a54e4d72c9a0d4de6537b4e07194009800..5c92dc8deb1135688aae58961f956a9a0e7cef9b 100644
--- a/Source/core/html/HTMLImageElement.h
+++ b/Source/core/html/HTMLImageElement.h
@@ -24,6 +24,7 @@
 #ifndef HTMLImageElement_h
 #define HTMLImageElement_h
 
+#include "core/frame/ViewportChangeNotifier.h"
 #include "core/html/HTMLElement.h"
 #include "core/html/HTMLImageLoader.h"
 #include "core/html/canvas/CanvasImageSource.h"
@@ -101,6 +102,36 @@ protected:
     virtual void didMoveToNewDocument(Document& oldDocument) OVERRIDE;
 
 private:
+    class ImageViewportChangeListener FINAL : public ViewportChangeListener {

[esprehn, 2014/07/14 08:39:50]

Why is the mediaQuery thing not handling this directly?

+    public:
+        static PassRefPtrWillBeRawPtr<ImageViewportChangeListener> create(HTMLImageElement* element)
+        {
+            return adoptRefWillBeNoop(new ImageViewportChangeListener(element));
+        }
+
+        virtual void viewportChanged() OVERRIDE
+        {
+            // Re-selecting the source URL in order to pick a more fitting resource
+            // And update the image's intrinsic dimensions when the viewport changes.
+            // Picking of a better fitting resource is UA dependant, not spec required.
+            m_element->selectSourceURL(ImageLoader::UpdateForce);
+        }
+
+        explicit ImageViewportChangeListener(HTMLImageElement* element)
+            : m_element(element)
+        {
+            ASSERT(element);
+        }
+
+        void trace(Visitor* visitor)

[sof, 2014/07/14 20:38:09]

This is an OVERRIDE (of ViewportChangeListener::trace()). Move the definition of
it into the .cpp file and manually delegate the trace() --

void trace(Visitor* visitor)
{
    visitor->trace(m_element);
    ViewportChangeListener::trace(visitor);
}

+        {
+            visitor->trace(m_element);
+        }
+
+    private:
+        RawPtrWillBeMember<HTMLImageElement> m_element;
+    };
+
     virtual bool areAuthorShadowsAllowed() const OVERRIDE { return false; }
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
@@ -141,6 +172,11 @@ private:
     float m_imageDevicePixelRatio;
     bool m_formWasSetByParser;
     bool m_elementCreatedByParser;
+    // Intrinsic sizing is viewport dependant if the 'w' descriptor was used for the picked resource.
+    bool m_intrinsicSizingViewportDependant;
+    // Effective size is viewport dependant if the sizes attribute's effective size used v* length units.
+    bool m_effectiveSizeViewportDependant;
+    RefPtrWillBeMember<ImageViewportChangeListener> m_viewportListener;

[esprehn, 2014/07/14 08:39:50]

I don't think we want to make every <img> bigger like this.

 };
 
 } //namespace