Revert "Removed default Isolate."

src/mksnapshot.cc

 // Copyright 2006-2008 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.
 
 #include <errno.h>
 #include <stdio.h>
 #ifdef COMPRESS_STARTUP_DATA_BZ2
 #include <bzlib.h>
 #endif
 #include <signal.h>
@@ skipping 375 matching lines @@
       writer.SetRawFiles(i::FLAG_raw_file, i::FLAG_raw_context_file);
 #ifdef COMPRESS_STARTUP_DATA_BZ2
     BZip2Compressor bzip2;
     writer.SetCompressor(&bzip2);
 #endif
     writer.WriteSnapshot(snapshot_data, ser, context_data, context_ser);
   }
 
   isolate->Exit();
   isolate->Dispose();
-  // TODO(svenpanne) Alas, we can't cleanly dispose V8 here, because
-  // Serializer::code_address_map_ is static (a.k.a. a global variable), and
-  // disposing that would involve accessing the Isolate just disposed.
-  // code_address_map_ really has to be an instance variable...
-  // V8::Dispose();
+  V8::Dispose();
   return 0;
 }