Compact weak fixed arrays before serializing.

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 2607 matching lines @@
  public:
   enum SearchForDuplicates { kAlwaysAdd, kAddIfNotFound };
 
   // If |maybe_array| is not a WeakFixedArray, a fresh one will be allocated.
   static Handle<WeakFixedArray> Add(
       Handle<Object> maybe_array, Handle<HeapObject> value,
       SearchForDuplicates search_for_duplicates = kAlwaysAdd);
 
   void Remove(Handle<HeapObject> value);
 
+  void Compact();
+
   inline Object* Get(int index) const;
   inline int Length() const;
 
   static Object* Empty() { return Smi::FromInt(0); }
 
   DECLARE_CAST(WeakFixedArray)
 
  private:
   static const int kLastUsedIndexIndex = 0;
   static const int kFirstIndex = 1;
@@ skipping 8449 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_