Add an experimental public API for value serialization.

src/value-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_VALUE_SERIALIZER_H_
 #define V8_VALUE_SERIALIZER_H_
 
 #include <cstdint>
 #include <vector>
 
@@ skipping 98 matching lines @@
  public:
   ValueDeserializer(Isolate* isolate, Vector<const uint8_t> data);
   ~ValueDeserializer();
 
   /*
    * Runs version detection logic, which may fail if the format is invalid.
    */
   Maybe<bool> ReadHeader() WARN_UNUSED_RESULT;
 
   /*
+   * Reads the underlying wire format version. Likely mostly to be useful to
+   * legacy code reading old wire format versions. Must be called after
+   * ReadHeader.
+   */
+  uint32_t GetWireFormatVersion() const { return version_; }
+
+  /*
    * Deserializes a V8 object from the buffer.
    */
   MaybeHandle<Object> ReadObject() WARN_UNUSED_RESULT;
 
   /*
    * Reads an object, consuming the entire buffer.
    *
    * This is required for the legacy "version 0" format, which did not allow
    * reference deduplication, and instead relied on a "stack" model for
    * deserializing, with the contents of objects and arrays provided first.
@@ skipping 43 matching lines @@
   Handle<SeededNumberDictionary> id_map_;  // Always a global handle.
   uint32_t next_id_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(ValueDeserializer);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_VALUE_SERIALIZER_H_