[serializer] split up src/snapshot/serialize.*

src/snapshot/startup-serializer.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_SNAPSHOT_STARTUP_SERIALIZER_H_
+#define V8_SNAPSHOT_STARTUP_SERIALIZER_H_
+
+#include "src/snapshot/serializer.h"
+
+namespace v8 {
+namespace internal {
+
+class StartupSerializer : public Serializer {
+ public:
+  StartupSerializer(Isolate* isolate, SnapshotByteSink* sink);
+  ~StartupSerializer() override;
+
+  // Serialize the current state of the heap.  The order is:
+  // 1) Strong references.
+  // 2) Partial snapshot cache.
+  // 3) Weak references (e.g. the string table).
+  void SerializeStrongReferences();
+  void SerializeWeakReferencesAndDeferred();
+
+ private:
+  // The StartupSerializer has to serialize the root array, which is slightly
+  // different.
+  void VisitPointers(Object** start, Object** end) override;
+  void SerializeObject(HeapObject* o, HowToCode how_to_code,
+                       WhereToPoint where_to_point, int skip) override;
+  void Synchronize(VisitorSynchronization::SyncTag tag) override;
+
+  intptr_t root_index_wave_front_;
+  bool serializing_builtins_;
+  DISALLOW_COPY_AND_ASSIGN(StartupSerializer);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_SNAPSHOT_STARTUP_SERIALIZER_H_