Simplify flattening to just write enough to call the factory

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 {
     typedef SkImageFilter INHERITED;
 
 public:
     static SkOffsetImageFilter* Create(SkScalar dx, SkScalar dy, SkImageFilter* input = NULL,
                                        const CropRect* cropRect = NULL) {
+        if (!SkScalarIsFinite(dx) || !SkScalarIsFinite(dy)) {
+            return NULL;
+        }
         return SkNEW_ARGS(SkOffsetImageFilter, (dx, dy, input, cropRect));
     }
     virtual void computeFastBounds(const SkRect& src, SkRect* dst) const SK_OVERRIDE;
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkOffsetImageFilter)
 
 protected:
     SkOffsetImageFilter(SkScalar dx, SkScalar dy, SkImageFilter* input, const CropRect* cropRect);
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
     explicit SkOffsetImageFilter(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;
     virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*) const SK_OVERRIDE;
 
 private:
     SkVector fOffset;
 };
 
 #endif