Simplify flattening to just write enough to call the factory

src/effects/SkTestImageFilters.cpp

 
 #include "SkTestImageFilters.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 // Simple helper canvas that "takes ownership" of the provided device, so that
 // when this canvas goes out of scope, so will its device. Could be replaced
 // with the following:
@@ skipping 53 matching lines @@
         OwnDeviceCanvas canvas(dev);
 
         SkRect r = SkRect::MakeWH(SkIntToScalar(src.width()),
                                   SkIntToScalar(src.height()));
         canvas.drawBitmapRect(tmp, NULL, r, NULL);
         *result = dev->accessBitmap(false);
     }
     return true;
 }
 
+SkFlattenable* SkDownSampleImageFilter::CreateProc(SkReadBuffer& buffer) {
+    SK_IMAGEFILTER_UNFLATTEN_COMMON(1);
+    return Create(buffer.readScalar(), common.inputAt(0));
+}
+
 void SkDownSampleImageFilter::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
-
     buffer.writeScalar(fScale);
 }
 
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
 SkDownSampleImageFilter::SkDownSampleImageFilter(SkReadBuffer& buffer)
   : INHERITED(1, buffer) {
     fScale = buffer.readScalar();
     buffer.validate(SkScalarIsFinite(fScale));
 }
+#endif