Reapply "Improve hashCode for closure objects" with fixes.

runtime/vm/clustered_snapshot.cc

 // Copyright (c) 2016, 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/clustered_snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 746 matching lines @@
                                      ClosureData::InstanceSize(), is_vm_object);
       if (d->kind() == Snapshot::kFullAOT) {
         data->ptr()->context_scope_ = ContextScope::null();
       } else {
         data->ptr()->context_scope_ =
             static_cast<RawContextScope*>(d->ReadRef());
       }
       data->ptr()->parent_function_ = static_cast<RawFunction*>(d->ReadRef());
       data->ptr()->signature_type_ = static_cast<RawType*>(d->ReadRef());
       data->ptr()->closure_ = static_cast<RawInstance*>(d->ReadRef());
-      data->ptr()->hash_ = Object::null();
     }
   }
 };
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
 class SignatureDataSerializationCluster : public SerializationCluster {
  public:
   SignatureDataSerializationCluster() {}
   virtual ~SignatureDataSerializationCluster() {}
 
@@ skipping 4752 matching lines @@
     thread_->isolate()->SetupImagePage(data_buffer_,
                                        /* is_executable */ false);
   }
 
   deserializer.ReadIsolateSnapshot(thread_->isolate()->object_store());
 
   return ApiError::null();
 }
 
 }  // namespace dart