Add DCHECKs to back reference deserialization.

src/serialize.h

 // Copyright 2012 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_SERIALIZE_H_
 #define V8_SERIALIZE_H_
 
 #include "src/compiler.h"
 #include "src/hashmap.h"
 #include "src/heap-profiler.h"
@@ skipping 207 matching lines @@
   AllocationSpace space() const {
     DCHECK(is_valid());
     return SpaceBits::decode(bitfield_);
   }
 
   uint32_t chunk_offset() const {
     DCHECK(is_valid());
     return ChunkOffsetBits::decode(bitfield_) << kObjectAlignmentBits;
   }
 
+  uint32_t large_object_index() const {
+    DCHECK(is_valid());
+    DCHECK(chunk_index() == 0);
+    return ChunkOffsetBits::decode(bitfield_);
+  }
+
   uint32_t chunk_index() const {
     DCHECK(is_valid());
     return ChunkIndexBits::decode(bitfield_);
   }
 
   uint32_t reference() const {
     DCHECK(is_valid());
     return bitfield_ & (ChunkOffsetBits::kMask | ChunkIndexBits::kMask);
   }
 
@@ skipping 454 matching lines @@
   bool SerializeKnownObject(HeapObject* obj, HowToCode how_to_code,
                             WhereToPoint where_to_point, int skip);
 
   inline void FlushSkip(int skip) {
     if (skip != 0) {
       sink_->Put(kSkip, "SkipFromSerializeObject");
       sink_->PutInt(skip, "SkipDistanceFromSerializeObject");
     }
   }
 
-  void InitializeAllocators();
+  bool BackReferenceIsAlreadyAllocated(BackReference back_reference);
+
   // This will return the space for an object.
   static AllocationSpace SpaceOfObject(HeapObject* object);
   BackReference AllocateLargeObject(int size);
   BackReference Allocate(AllocationSpace space, int size);
   int EncodeExternalReference(Address addr) {
     return external_reference_encoder_->Encode(addr);
   }
 
   // GetInt reads 4 bytes at once, requiring padding at the end.
   void Pad();
@@ skipping 252 matching lines @@
   static const int kFlagHashOffset = 3;
   static const int kNumInternalizedStringsOffset = 4;
   static const int kReservationsOffset = 5;
   static const int kNumCodeStubKeysOffset = 6;
   static const int kPayloadLengthOffset = 7;
   static const int kHeaderSize = (kPayloadLengthOffset + 1) * kIntSize;
 };
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_