In background compilation make a copy of Field in order to freeze its state

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/bootstrap.h"
 #include "vm/compiler.h"
 #include "vm/constant_propagator.h"
@@ skipping 401 matching lines @@
 }
 
 
 ConstantInstr::ConstantInstr(const Object& value, TokenPosition token_pos)
     : value_(value),
       token_pos_(token_pos) {
   // Check that the value is not an incorrect Integer representation.
   ASSERT(!value.IsBigint() || !Bigint::Cast(value).FitsIntoSmi());
   ASSERT(!value.IsBigint() || !Bigint::Cast(value).FitsIntoInt64());
   ASSERT(!value.IsMint() || !Smi::IsValid(Mint::Cast(value).AsInt64Value()));
+  ASSERT(!value.IsField() || Field::Cast(value).IsOriginal());
 }
 
 
 bool ConstantInstr::AttributesEqual(Instruction* other) const {
   ConstantInstr* other_constant = other->AsConstant();
   ASSERT(other_constant != NULL);
   return (value().raw() == other_constant->value().raw());
 }
 
 
@@ skipping 3292 matching lines @@
   set_native_c_function(native_function);
   function().SetIsNativeAutoSetupScope(auto_setup_scope);
   Dart_NativeEntryResolver resolver = library.native_entry_resolver();
   bool is_bootstrap_native = Bootstrap::IsBootstapResolver(resolver);
   set_is_bootstrap_native(is_bootstrap_native);
 }
 
 #undef __
 
 }  // namespace dart