Don't serialize anything for SkEmptyShader.

src/core/SkEmptyShader.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkEmptyShader_DEFINED
 #define SkEmptyShader_DEFINED
 
@@ skipping 16 matching lines @@
     }
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkEmptyShader)
 
 protected:
     SkShader::Context* onCreateContext(const ContextRec&, void*) const override {
         return NULL;
     }
 
+    void flatten(SkWriteBuffer& buffer) const override {
+        // Do nothing.
+        // We just don't want to fall through to SkShader::flatten(),
+        // which will write data we don't care to serialize or decode.
+    }
+
 private:
     typedef SkShader INHERITED;
 };
 
 #endif