Reapply "Improve hashCode for closure objects" with fixes.

runtime/vm/isolate_reload.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/isolate_reload.h"
 
 #include "vm/become.h"
 #include "vm/bit_vector.h"
 #include "vm/compiler.h"
 #include "vm/dart_api_impl.h"
@@ skipping 339 matching lines @@
     if (obj.IsLibrary()) {
       return Library::Cast(obj).UrlHash();
     } else if (obj.IsClass()) {
       if (Class::Cast(obj).id() == kFreeListElement) {
         return 0;
       }
       return String::HashRawSymbol(Class::Cast(obj).Name());
     } else if (obj.IsField()) {
       return String::HashRawSymbol(Field::Cast(obj).name());
     } else if (obj.IsInstance()) {
-      return Smi::Handle(Smi::RawCast(Instance::Cast(obj).HashCode())).Value();
+      Object& hashObj = Object::Handle(Instance::Cast(obj).HashCode());
+      if (hashObj.IsError()) {
+        Exceptions::PropagateError(Error::Cast(hashObj));
+      }
+      return Smi::Cast(hashObj).Value();
     }
     return 0;
   }
 };
 
 bool IsolateReloadContext::IsSameField(const Field& a, const Field& b) {
   if (a.is_static() != b.is_static()) {
     return false;
   }
   const Class& a_cls = Class::Handle(a.Owner());
@@ skipping 1447 matching lines @@
         ASSERT(!super_cls.IsNull());
         super_cls.AddDirectSubclass(cls);
       }
     }
   }
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart