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..bf0fa1a6e8d9846b760598ce5154fc636c33043b 100644
--- a/Source/core/html/HTMLImageElement.h
+++ b/Source/core/html/HTMLImageElement.h
@@ -34,9 +34,12 @@ namespace WebCore {
 
 class HTMLFormElement;
 class ImageCandidate;
+class MediaQueryList;
 
 class HTMLImageElement FINAL : public HTMLElement, public CanvasImageSource {
 public:
+    class Listener;
+
     static PassRefPtrWillBeRawPtr<HTMLImageElement> create(Document&);
     static PassRefPtrWillBeRawPtr<HTMLImageElement> create(Document&, HTMLFormElement*, bool createdByParser);
     static PassRefPtrWillBeRawPtr<HTMLImageElement> createForJSConstructor(Document&, int width, int height);
@@ -129,6 +132,8 @@ private:
     ImageCandidate findBestFitImageFromPictureParent();
     void setBestFitURLAndDPRFromImageCandidate(const ImageCandidate&);
     HTMLImageLoader& imageLoader() const { return *m_imageLoader; }
+    void notifyMediaQueryChanged();
+    void createMediaQueryListIfDoesNotExist();
 
     OwnPtrWillBeMember<HTMLImageLoader> m_imageLoader;
 #if ENABLE(OILPAN)
@@ -141,6 +146,12 @@ 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<Listener> m_listener;

[sof, 2014/07/15 10:27:30]

Whenever a traceable Member is added to a class, you need to trace() it in the
class' trace() method. Both the Members here aren't traced.

+    RefPtrWillBeMember<MediaQueryList> m_mediaQueryList;
 };

[Yoav Weiss, 2014/07/15 09:46:31]

If the extra memory on HTMLImageElement is an issue here (considering that
m_listener and m_mediaQueryList) are created only for images that need them, I'd
appreciate some advice on how to reduce that footprint.
Possible optimizations include:
* Instruct the compiler to pack the 4 booleans on HTMLImageElement.
* Create a single raw pointer that would hold both m_listener and
m_mediaQueryList. (Note that they are created only when they are actually
needed, so when the image is viewport dependent)
* Avoid storing m_mediaQueryList and create it each time the source is
recalculated.

 
 } //namespace