Allow eviction of ImageBitmaps that are created from ImageElements.

Source/core/loader/cache/MemoryCache.h

Index: Source/core/loader/cache/MemoryCache.h
diff --git a/Source/core/loader/cache/MemoryCache.h b/Source/core/loader/cache/MemoryCache.h
index 95b136ef8e7b838bc22174069a0e8e376ff88b6d..1a257a59bb3f57e2ae3ad782e0a3bb8af4e611f0 100644
--- a/Source/core/loader/cache/MemoryCache.h
+++ b/Source/core/loader/cache/MemoryCache.h
@@ -25,6 +25,7 @@
 #ifndef Cache_h
 #define Cache_h
 
+#include "core/platform/Timer.h"
 #include "wtf/HashMap.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/Vector.h"
@@ -119,6 +120,7 @@ public:
     //  - maxDeadBytes: The maximum number of bytes that dead resources should consume when the cache is not under pressure.
     //  - totalBytes: The maximum number of bytes that the cache should consume overall.
     void setCapacities(unsigned minDeadBytes, unsigned maxDeadBytes, unsigned totalBytes);
+    void setDelayBeforeLiveDecodedPrune(unsigned seconds) { m_delayBeforeLiveDecodedPrune = seconds; }
 
     void evictResources();
 
@@ -184,6 +186,7 @@ private:
     unsigned m_minDeadCapacity;
     unsigned m_maxDeadCapacity;
     double m_deadDecodedDataDeletionInterval;
+    unsigned m_delayBeforeLiveDecodedPrune;
 
     unsigned m_liveSize; // The number of bytes currently consumed by "live" resources in the cache.
     unsigned m_deadSize; // The number of bytes currently consumed by "dead" resources in the cache.
@@ -193,8 +196,9 @@ private:
     // waiting to die when the clients referencing them go away.
     Vector<LRUList, 32> m_allResources;
     
-    // List just for live resources with decoded data.  Access to this list is based off of painting the resource.
-    LRUList m_liveDecodedResources;
+    // Lists just for live resources with decoded data. Access to this list is based off of painting the resource.
+    // The lists are ordered by decode priority, with higher indices having higher priorities.
+    LRUList m_liveDecodedResources[3];
     
     // A URL-based map of all resources that are in the cache (including the freshest version of objects that are currently being 
     // referenced by a Web page).