retool image cache to be generic cache

src/lazy/SkCachingPixelRef.h

Index: src/lazy/SkCachingPixelRef.h
diff --git a/src/lazy/SkCachingPixelRef.h b/src/lazy/SkCachingPixelRef.h
index 1e87874f74dd5d2ec151cd24652d01ad6feadf40..0f78ce99bff6679fb2fc8f1850b9fe5e4b2c11dd 100644
--- a/src/lazy/SkCachingPixelRef.h
+++ b/src/lazy/SkCachingPixelRef.h
@@ -8,6 +8,7 @@
 #ifndef SkCachingPixelRef_DEFINED
 #define SkCachingPixelRef_DEFINED
 
+#include "SkBitmapCache.h"
 #include "SkImageInfo.h"
 #include "SkImageGenerator.h"
 #include "SkPixelRef.h"
@@ -52,7 +53,7 @@ protected:
 private:
     SkImageGenerator* const fImageGenerator;
     bool                    fErrorInDecoding;
-    void*                   fScaledCacheId;
+    SkBitmapCache::ID       fScaledCacheId;
     const size_t            fRowBytes;
 
     SkCachingPixelRef(const SkImageInfo&, SkImageGenerator*, size_t rowBytes);