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 e78d90364d3f16c1314c4fe448b17308a075e32b..a0cf2a1f945562316ba991c3fd0636ed46f7cbff 100644
--- a/Source/core/loader/cache/CachedResource.h
+++ b/Source/core/loader/cache/CachedResource.h
@@ -80,6 +80,12 @@ public:
         DecodeError
     };
 
+    enum DecodePriority {

[Justin Novosad, 2013/07/23 16:55:12]

Hmmm... this name sounds like it determines which image will be decoded before
the others, which is not what it is for. How about calling it CachePriority?

+        DecodePriorityLow = 0,
+        DecodePriorityMedium,
+        DecodePriorityHigh
+    };
+
     CachedResource(const ResourceRequest&, Type);
     virtual ~CachedResource();
 
@@ -169,6 +175,8 @@ public:
     void setInCache(bool inCache) { m_inCache = inCache; }
     bool inCache() const { return m_inCache; }
     
+    void setDecodePriority(DecodePriority);
+    DecodePriority decodePriority() const { return m_decodePriority; }
     bool inLiveDecodedResourcesList() { return m_inLiveDecodedResourcesList; }
     
     void clearLoader();
@@ -317,6 +325,7 @@ private:
 
     unsigned m_preloadResult : 2; // PreloadResult
 
+    DecodePriority m_decodePriority;
     bool m_inLiveDecodedResourcesList : 1;
     bool m_requestedFromNetworkingLayer : 1;