Add support for serializing/deserializing of SkDrawable

include/core/SkDrawable.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDrawable_DEFINED
 #define SkDrawable_DEFINED
 
-#include "SkRefCnt.h"
+#include "SkFlattenable.h"
 
 class SkCanvas;
 class SkPicture;
 struct SkRect;
 
 /**
  *  Base-class for objects that draw into SkCanvas.
  *
  *  The object has a generation ID, which is guaranteed to be unique across all drawables. To
  *  allow for clients of the drawable that may want to cache the results, the drawable must
  *  change its generation ID whenever its internal state changes such that it will draw differently.
  */
-class SkDrawable : public SkRefCnt {
+class SkDrawable : public SkFlattenable {
 public:
     SkDrawable();
 
     /**
      *  Draws into the specified content. The drawing sequence will be balanced upon return
      *  (i.e. the saveLevel() on the canvas will match what it was when draw() was called,
      *  and the current matrix and clip settings will not be changed.
      */
     void draw(SkCanvas*, const SkMatrix* = NULL);
     void draw(SkCanvas*, SkScalar x, SkScalar y);
@@ skipping 16 matching lines @@
      */
     SkRect getBounds();
 
     /**
      *  Calling this invalidates the previous generation ID, and causes a new one to be computed
      *  the next time getGenerationID() is called. Typically this is called by the object itself,
      *  in response to its internal state changing.
      */
     void notifyDrawingChanged();
 
+    SK_DEFINE_FLATTENABLE_TYPE(SkDrawable)
+    virtual Factory getFactory() const { return nullptr; }
+
 protected:
     virtual SkRect onGetBounds() = 0;
     virtual void onDraw(SkCanvas*) = 0;
     
     /**
      *  Default implementation calls onDraw() with a canvas that records into a picture. Subclasses
      *  may override if they have a more efficient way to return a picture for the current state
      *  of their drawable. Note: this picture must draw the same as what would be drawn from
      *  onDraw().
      */
     virtual SkPicture* onNewPictureSnapshot();
 
 private:
     int32_t fGenerationID;
 };
 
 #endif