don't use default isolate in mksnapshot

src/serialize.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1266 matching lines @@
 
 
 Serializer::Serializer(Isolate* isolate, SnapshotByteSink* sink)
     : isolate_(isolate),
       sink_(sink),
       current_root_index_(0),
       external_reference_encoder_(new ExternalReferenceEncoder(isolate)),
       root_index_wave_front_(0) {
   // The serializer is meant to be used only to generate initial heap images
   // from a context in which there is only one isolate.
-  ASSERT(isolate_->IsDefaultIsolate());
   for (int i = 0; i <= LAST_SPACE; i++) {
     fullness_[i] = 0;
   }
 }
 
 
 Serializer::~Serializer() {
   delete external_reference_encoder_;
 }
 
@@ skipping 558 matching lines @@
 
 bool SnapshotByteSource::AtEOF() {
   if (0u + length_ - position_ > 2 * sizeof(uint32_t)) return false;
   for (int x = position_; x < length_; x++) {
     if (data_[x] != SerializerDeserializer::nop()) return false;
   }
   return true;
 }
 
 } }  // namespace v8::internal