Update SkImageFilter's cache to handle SkSpecialImages and add unit test

include/core/SkImageFilter.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageFilter_DEFINED
 #define SkImageFilter_DEFINED
 
 #include "../private/SkTArray.h"
 #include "../private/SkTemplates.h"
 #include "../private/SkMutex.h"
 #include "SkFilterQuality.h"
 #include "SkFlattenable.h"
 #include "SkMatrix.h"
 #include "SkRect.h"
 #include "SkSurfaceProps.h"
 
 class GrFragmentProcessor;
 class GrTexture;
 class SkBaseDevice;
 class SkBitmap;
 class SkColorFilter;
 struct SkIPoint;
+class SkSpecialImage;
 
 /**
  *  Base class for image filters. If one is installed in the paint, then
  *  all drawing occurs as usual, but it is as if the drawing happened into an
  *  offscreen (before the xfermode is applied). This offscreen bitmap will
  *  then be handed to the imagefilter, who in turn creates a new bitmap which
  *  is what will finally be drawn to the device (using the original xfermode).
  */
 class SK_API SkImageFilter : public SkFlattenable {
 public:
     // This cache maps from (filter's unique ID + CTM + clipBounds + src bitmap generation ID) to
     // (result, offset).
     class Cache : public SkRefCnt {
     public:
         struct Key;
         virtual ~Cache() {}
         static Cache* Create(size_t maxBytes);
         static Cache* Get();
         virtual bool get(const Key& key, SkBitmap* result, SkIPoint* offset) const = 0;
+        virtual SkSpecialImage* get(const Key& key, SkIPoint* offset) const = 0;
         virtual void set(const Key& key, const SkBitmap& result, const SkIPoint& offset) = 0;
+        virtual void set(const Key& key, SkSpecialImage* image, const SkIPoint& offset) = 0;
         virtual void purge() {}
         virtual void purgeByKeys(const Key[], int) {}
     };
 
     class Context {
     public:
         Context(const SkMatrix& ctm, const SkIRect& clipBounds, Cache* cache)
             : fCTM(ctm)
             , fClipBounds(clipBounds)
             , fCache(cache)
@@ skipping 405 matching lines @@
  */
 #define SK_IMAGEFILTER_UNFLATTEN_COMMON(localVar, expectedCount)    \
     Common localVar;                                                \
     do {                                                            \
         if (!localVar.unflatten(buffer, expectedCount)) {           \
             return NULL;                                            \
         }                                                           \
     } while (0)
 
 #endif