Implement support for a Context parameter in image filters

include/effects/SkTestImageFilters.h

 #ifndef _SkTestImageFilters_h
 #define _SkTestImageFilters_h
 
 #include "SkImageFilter.h"
 #include "SkPoint.h"
 
 // Fun mode that scales down (only) and then scales back up to look pixelated
 class SK_API SkDownSampleImageFilter : public SkImageFilter {
 public:
     static SkDownSampleImageFilter* Create(SkScalar scale) {
         return SkNEW_ARGS(SkDownSampleImageFilter, (scale));
     }
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDownSampleImageFilter)
 
 protected:
     SkDownSampleImageFilter(SkScalar scale) : INHERITED(0), fScale(scale) {}
     SkDownSampleImageFilter(SkReadBuffer& buffer);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
-    virtual bool onFilterImage(Proxy*, const SkBitmap& src, const SkMatrix&,
+    virtual bool onFilterImage(Proxy*, const SkBitmap& src, const Context&,
                                SkBitmap* result, SkIPoint* loc) const SK_OVERRIDE;
 
 private:
     SkScalar fScale;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif