add scaledimagecache

src/core/SkScaledImageCache.h

+#ifndef SkScaledImageCache_DEFINED
+#define SkScaledImageCache_DEFINED
+
+#include "SkBitmap.h"
+
+class SkScaledImageCache {
+public:
+    struct ID;
+
+    /**
+     *  Search the cache for a scaled version of original. If found, return it
+     *  in scaled, and return its ID pointer. Use the returned ptr to unlock
+     *  the cache when you are done using scaled.
+     *
+     *  If a match is not found, scaled will be unmodifed, and NULL will be
+     *  returned.
+     */
+    static ID* FindAndLock(const SkBitmap& original, SkScalar scaleX,
+                           SkScalar scaleY, SkBitmap* scaled);
+
+    /**
+     *  To add a new (scaled) bitmap to the cache, call AddAndLock. Use the
+     *  returned ptr to unlock the cache when you are done using scaled.
+     */
+    static ID* AddAndLock(const SkBitmap& original, SkScalar scaleX,
+                           SkScalar scaleY, const SkBitmap& scaled);
+
+    static void Unlock(ID*);
+
+    static size_t GetByteLimit();
+    static size_t SetByteLimit(size_t newLimit);
+    static size_t GetBytesUsed();
+
+    SkScaledImageCache();
+    ~SkScaledImageCache();
+    
+private:
+    ID* findAndLock(const SkBitmap& original, SkScalar scaleX,
+                    SkScalar scaleY, SkBitmap* scaled);
+    ID* addAndLock(const SkBitmap& original, SkScalar scaleX,
+                   SkScalar scaleY, const SkBitmap& scaled);
+    void unlock(ID*);
+
+    struct Rec;
+    Rec*    fHead;
+    Rec*    fTail;
+
+    size_t  fBytesUsed;
+    size_t  fByteLimit;
+    int     fCount;
+
+    void purgeAsNeeded();
+
+    // linklist management
+    void moveToHead(Rec*);
+    void addToHead(Rec*);
+    void detach(Rec*);
+#ifdef SK_DEBUG
+    void validate() const;
+#else
+    void validate() const {}
+#endif
+};
+
+#endif