Reapply "Improve hashCode for closure objects" with fixes.

runtime/vm/raw_object_snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
@@ skipping 566 matching lines @@
                                       bool as_reference) {
   ASSERT(reader != NULL);
   ASSERT(kind == Snapshot::kScript);
 
   // Allocate closure data object.
   ClosureData& data =
       ClosureData::ZoneHandle(reader->zone(), ClosureData::New());
   reader->AddBackRef(object_id, &data, kIsDeserialized);
 
   // Set all the object fields.
-  // Cached hash is null-initialized by ClosureData::New()
   READ_OBJECT_FIELDS(data, data.raw()->from(), data.raw()->to_snapshot(),
                      kAsInlinedObject);
 
   return data.raw();
 }
 
 void RawClosureData::WriteTo(SnapshotWriter* writer,
                              intptr_t object_id,
                              Snapshot::Kind kind,
                              bool as_reference) {
@@ skipping 2322 matching lines @@
     // We do not allow objects with native fields in an isolate message.
     writer->SetWriteException(Exceptions::kArgument,
                               "Illegal argument in isolate message"
                               " : (object is a UserTag)");
   } else {
     UNREACHABLE();
   }
 }
 
 }  // namespace dart