Move Image ownership out of CSSValue

Source/core/css/resolver/ElementStyleResources.h

Index: Source/core/css/resolver/ElementStyleResources.h
diff --git a/Source/core/css/resolver/ElementStyleResources.h b/Source/core/css/resolver/ElementStyleResources.h
index c4b267f584dd483af74d1bf04a7b25098dce2c92..9a8a597a79cedeb7f5bfe585a009bdd62cf637bd 100644
--- a/Source/core/css/resolver/ElementStyleResources.h
+++ b/Source/core/css/resolver/ElementStyleResources.h
@@ -24,6 +24,7 @@
 #define ElementStyleResources_h
 
 #include "core/CSSPropertyNames.h"
+#include "core/style/StyleImage.h"
 #include "platform/graphics/Color.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashMap.h"
@@ -61,9 +62,12 @@ public:
 
     const PendingImagePropertyMap& pendingImageProperties() const { return m_pendingImageProperties; }
     const PendingSVGDocumentMap& pendingSVGDocuments() const { return m_pendingSVGDocuments; }
+    const CSSStyleImageMap& cssImages() const { return m_cssImages; }
+    CSSStyleImageMap& mutableCssImages() { return m_cssImages; }
 
     void clearPendingImageProperties();
     void clearPendingSVGDocuments();
+    void clearCSSImages();
 
     float deviceScaleFactor() const { return m_deviceScaleFactor; }
     void setDeviceScaleFactor(float deviceScaleFactor) { m_deviceScaleFactor = deviceScaleFactor; }
@@ -73,6 +77,10 @@ public:
 private:
     PendingImagePropertyMap m_pendingImageProperties;
     PendingSVGDocumentMap m_pendingSVGDocuments;
+
+    // A list of all the images referenced by CSS
+    CSSStyleImageMap m_cssImages;
+
     float m_deviceScaleFactor;
 };