Implement a persistent uniqueID-based cache for SkImageFilter.

include/core/SkDevice.h

 /*
  * Copyright 2010 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDevice_DEFINED
 #define SkDevice_DEFINED
 
@@ skipping 360 matching lines @@
     SkBaseDevice* createCompatibleDeviceForSaveLayer(const SkImageInfo&);
 
     virtual SkBaseDevice* onCreateDevice(const SkImageInfo&, Usage) {
         return NULL;
     }
 
     /** Causes any deferred drawing to the device to be completed.
      */
     virtual void flush() {}
 
+    virtual SkImageFilter::UniqueIDCache* getImageFilterCache() { return NULL; }
+
     SkIPoint    fOrigin;
     SkMetaData* fMetaData;
 
 #ifdef SK_DEBUG
     bool        fAttachedToCanvas;
 #endif
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif