[serializer] introduce API to serialize internal fields

src/snapshot/serializer-common.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_SERIALIZER_COMMON_H_
 #define V8_SNAPSHOT_SERIALIZER_COMMON_H_
 
 #include "src/address-map.h"
 #include "src/external-reference-table.h"
 #include "src/globals.h"
@@ skipping 154 matching lines @@
   static const int kVariableRawData = 0x1a;
   // Internal reference encoded as offsets of pc and target from code entry.
   static const int kInternalReference = 0x1b;
   static const int kInternalReferenceEncoded = 0x1c;
   // Used for the source code of the natives, which is in the executable, but
   // is referred to from external strings in the snapshot.
   static const int kNativesStringResource = 0x1d;
   // Used for the source code for compiled stubs, which is in the executable,
   // but is referred to from external strings in the snapshot.
   static const int kExtraNativesStringResource = 0x1e;
+  // Used for embedder-provided serialization data for internal fields.
+  static const int kInternalFieldsData = 0x1f;
 
   // 8 hot (recently seen or back-referenced) objects with optional skip.
   static const int kNumberOfHotObjects = 8;
   STATIC_ASSERT(kNumberOfHotObjects == HotObjectsList::kSize);
   // 0x38..0x3f
   static const int kHotObject = 0x38;
   // 0x58..0x5f
   static const int kHotObjectWithSkip = 0x58;
   static const int kHotObjectMask = 0x07;
 
-  // 0x1f, 0x35..0x37, 0x55..0x57, 0x75..0x7f unused.
+  // 0x35..0x37, 0x55..0x57, 0x75..0x7f unused.
 
   // ---------- byte code range 0x80..0xff ----------
   // First 32 root array items.
   static const int kNumberOfRootArrayConstants = 0x20;
   // 0x80..0x9f
   static const int kRootArrayConstants = 0x80;
   // 0xa0..0xbf
   static const int kRootArrayConstantsWithSkip = 0xa0;
   static const int kRootArrayConstantsMask = 0x1f;
 
@@ skipping 82 matching lines @@
 
   byte* data_;
   int size_;
   bool owns_data_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_SERIALIZER_COMMON_H_