Clean up SkImageFilter constructors.

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));
+    static SkDownSampleImageFilter* Create(SkScalar scale, SkImageFilter* input = NULL) {
+        return SkNEW_ARGS(SkDownSampleImageFilter, (scale, input));
     }
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDownSampleImageFilter)
 
 protected:
-    SkDownSampleImageFilter(SkScalar scale) : INHERITED(0), fScale(scale) {}
+    SkDownSampleImageFilter(SkScalar scale, SkImageFilter* input)
+      : INHERITED(1, &input), fScale(scale) {}
     SkDownSampleImageFilter(SkReadBuffer& buffer);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
     virtual bool onFilterImage(Proxy*, const SkBitmap& src, const Context&,
                                SkBitmap* result, SkIPoint* loc) const SK_OVERRIDE;
 
 private:
     SkScalar fScale;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif