retool image cache to be generic cache

src/lazy/SkCachingPixelRef.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCachingPixelRef.h"
 #include "SkBitmapCache.h"
 
@@ skipping 70 matching lines @@
     // reference to the concrete PixelRef while this record is
     // locked.
     rec->fPixels = pixels;
     rec->fColorTable = NULL;
     rec->fRowBytes = bitmap.rowBytes();
     return true;
 }
 
 void SkCachingPixelRef::onUnlockPixels() {
     SkASSERT(fScaledCacheId != NULL);
-    SkScaledImageCache::Unlock( static_cast<SkScaledImageCache::ID*>(fScaledCacheId));
+    SkScaledImageCache::Unlock(fScaledCacheId);
     fScaledCacheId = NULL;
 }