Get OffsetImageFilter really working with SkSpecialImages

include/effects/SkOffsetImageFilter.h

 /*
  * Copyright 2012 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 SkOffsetImageFilter_DEFINED
 #define SkOffsetImageFilter_DEFINED
 
 #include "SkImageFilter.h"
 #include "SkPoint.h"
 
 class SK_API SkOffsetImageFilter : public SkImageFilter {
 public:
     static SkImageFilter* Create(SkScalar dx, SkScalar dy, SkImageFilter* input = NULL,
                                  const CropRect* cropRect = NULL) {
         if (!SkScalarIsFinite(dx) || !SkScalarIsFinite(dy)) {
             return NULL;
         }
         return new SkOffsetImageFilter(dx, dy, input, cropRect);
     }
 
     void computeFastBounds(const SkRect& src, SkRect* dst) const override;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkOffsetImageFilter)
 
+    // TODO: remove this when all the image filters are converted
+    bool supportsUnifiedFiltering() const override { return true; }
+
 protected:
     void flatten(SkWriteBuffer&) const override;
     bool onFilterImageDeprecated(Proxy*, const SkBitmap& src, const Context&, SkBitmap* result,
                                  SkIPoint* loc) const override;
+    SkSpecialImage* onFilterImage(SkSpecialImage* src, const Context&,
+                                  SkIPoint* offset) const override;
     void onFilterNodeBounds(const SkIRect&, const SkMatrix&, SkIRect*, MapDirection) const override;
 
 private:
     SkOffsetImageFilter(SkScalar dx, SkScalar dy, SkImageFilter* input, const CropRect*);
 
     SkVector fOffset;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif