Simplify flattening to just write enough to call the factory

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, SkImageFilter* input = NULL) {
+        if (!SkScalarIsFinite(scale)) {
+            return NULL;
+        }
+        // we don't support scale in this range
+        if (scale > SK_Scalar1 || scale <= 0) {
+            return NULL;
+        }
         return SkNEW_ARGS(SkDownSampleImageFilter, (scale, input));
     }
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDownSampleImageFilter)
 
 protected:
     SkDownSampleImageFilter(SkScalar scale, SkImageFilter* input)
       : INHERITED(1, &input), fScale(scale) {}
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
     SkDownSampleImageFilter(SkReadBuffer& buffer);
+#endif
     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