Allow eviction of ImageBitmaps that are created from ImageElements.

Source/core/loader/ImageLoader.h

Index: Source/core/loader/ImageLoader.h
diff --git a/Source/core/loader/ImageLoader.h b/Source/core/loader/ImageLoader.h
index f06089e2e5ae62f7eea6a4e8c991302d79b64284..92f450981942022964f173f91a189da70e25b2d3 100644
--- a/Source/core/loader/ImageLoader.h
+++ b/Source/core/loader/ImageLoader.h
@@ -26,10 +26,19 @@
 #include "core/loader/cache/CachedImage.h"
 #include "core/loader/cache/CachedImageClient.h"
 #include "core/loader/cache/CachedResourceHandle.h"
+#include "wtf/HashSet.h"
 #include "wtf/text/AtomicString.h"
 
 namespace WebCore {
 
+class ImageLoaderClient {
+public:
+    virtual void notifyImageSourceChanged() { }
+
+protected:
+    ImageLoaderClient() { }
+};
+
 class Element;
 class ImageLoader;
 class RenderImageResource;
@@ -69,6 +78,9 @@ public:
     static void dispatchPendingLoadEvents();
     static void dispatchPendingErrorEvents();
 
+    void addClient(ImageLoaderClient* client) { m_clients.add(client); }

[Stephen White, 2013/07/25 18:01:07]

I'm not sure if the ImageLoader is really the right place for this, since it's
not really related to image loading per se. IIUC, you want to watch changes to
the Image element's src attribute. I'm wondering if there's an observer or
something at the DOM level that you could use for this.

+    void removeClient(ImageLoaderClient* client) { m_clients.remove(client); }
+
 protected:
     virtual void notifyFinished(CachedResource*);
 
@@ -86,12 +98,14 @@ private:
     void updateRenderer();
 
     void setImageWithoutConsideringPendingLoadEvent(CachedImage*);
+    void sourceImageChanged();
     void clearFailedLoadURL();
 
     void timerFired(Timer<ImageLoader>*);
 
     Element* m_element;
     CachedResourceHandle<CachedImage> m_image;
+    HashSet<ImageLoaderClient*> m_clients;
     Timer<ImageLoader> m_derefElementTimer;
     AtomicString m_failedLoadURL;
     bool m_hasPendingBeforeLoadEvent : 1;