Allow eviction of ImageBitmaps that are created from ImageElements.

Source/core/loader/cache/CachedResource.h

Index: Source/core/loader/cache/CachedResource.h
diff --git a/Source/core/loader/cache/CachedResource.h b/Source/core/loader/cache/CachedResource.h
index b9c6f778fcd40d7247d28aa2c579a2d346087cf5..606813244f92c8c577a2bc1f4a6b2314cb89f413 100644
--- a/Source/core/loader/cache/CachedResource.h
+++ b/Source/core/loader/cache/CachedResource.h
@@ -80,6 +80,12 @@ public:
         DecodeError
     };
 
+    enum CachePriority {
+        CachePriorityLow = 0,
+        CachePriorityMedium,
+        CachePriorityHigh
+    };
+
     CachedResource(const ResourceRequest&, Type);
     virtual ~CachedResource();
 
@@ -167,6 +173,8 @@ public:
     void setInCache(bool inCache) { m_inCache = inCache; }
     bool inCache() const { return m_inCache; }
     
+    void setCachePriority(CachePriority);
+    unsigned cachePriority() const { return m_cachePriority; }
     bool inLiveDecodedResourcesList() { return m_inLiveDecodedResourcesList; }
     
     void clearLoader();
@@ -310,6 +318,7 @@ private:
     unsigned m_preloadCount;
 
     unsigned m_preloadResult : 2; // PreloadResult
+    unsigned m_cachePriority : 2; // CachePriority
 
     bool m_inLiveDecodedResourcesList : 1;
     bool m_requestedFromNetworkingLayer : 1;