Add support for serializing/deserializing of SkDrawable

src/core/SkSerializeDrawable.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkDrawable.h"
+#include "SkReadBuffer.h"
+#include "SkWriteBuffer.h"
+
+class SkSerializeDrawable {
+public:
+
+    /**
+     *  Create an SkDrawable from serialized data.
+     */
+    static SkDrawable* NewFromSerialized(SkReadBuffer& buffer) {
+        return (SkDrawable*) buffer.readFlattenable(SkFlattenable::kSkDrawable_Type);
+    }
+
+    /**
+     *  Serialize an SkDrawable.
+     */
+    static SkWriteBuffer* Serialize(const SkDrawable& drawable) {
+        SkWriteBuffer* buffer = new SkWriteBuffer();
+        buffer->writeFlattenable(&drawable);
+        return buffer;
+    }
+};