Add support for serializing/deserializing of SkDrawable

include/core/SkFlattenable.h

 /*
  * Copyright 2006 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 SkFlattenable_DEFINED
 #define SkFlattenable_DEFINED
 
@@ skipping 53 matching lines @@
 /** \class SkFlattenable
 
  SkFlattenable is the base class for objects that need to be flattened
  into a data stream for either transport or as part of the key to the
  font cache.
  */
 class SK_API SkFlattenable : public SkRefCnt {
 public:
     enum Type {
         kSkColorFilter_Type,
+        kSkDrawable_Type,

[reed1, 2016/03/31 18:42:05]

do we ever serialize this enum, in which case renumbering them would be tricky?

[msarett, 2016/04/01 14:11:44]

No we don't serialize the enums.  They don't do much... I actually considered a
CL to delete them.
https://codereview.chromium.org/1834303003/

But they seem pretty harmless, and can be used to suggest casts or for
validation.

         kSkDrawLooper_Type,
         kSkImageFilter_Type,
         kSkMaskFilter_Type,
         kSkPathEffect_Type,
         kSkPixelRef_Type,
         kSkRasterizer_Type,
         kSkShader_Type,
         kSkUnused_Type,     // used to be SkUnitMapper
         kSkXfermode_Type,
     };
@@ skipping 33 matching lines @@
 
 private:
     static void InitializeFlattenablesIfNeeded();
 
     friend class SkGraphics;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif