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

runtime/vm/flow_graph_builder.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/flow_graph_builder.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/compiler.h"
@@ skipping 2752 matching lines @@
   BuildClosureCall(node, false);
 }
 
 
 void ValueGraphVisitor::VisitClosureCallNode(ClosureCallNode* node) {
   BuildClosureCall(node, true);
 }
 
 
 void EffectGraphVisitor::VisitInitStaticFieldNode(InitStaticFieldNode* node) {
-  Value* field = Bind(new(Z) ConstantInstr(node->field()));
+  Value* field = Bind(new(Z) ConstantInstr(
+      Field::ZoneHandle(Z, node->field().Original())));
   AddInstruction(new(Z) InitStaticFieldInstr(field, node->field()));
 }
 
 
 void EffectGraphVisitor::VisitCloneContextNode(CloneContextNode* node) {
   Value* context = Bind(BuildCurrentContext(node->token_pos()));
   Value* clone = Bind(new(Z) CloneContextInstr(node->token_pos(), context));
   Do(BuildStoreContext(clone, node->token_pos()));
 }
 
@@ skipping 942 matching lines @@
 void EffectGraphVisitor::VisitLoadStaticFieldNode(LoadStaticFieldNode* node) {
   const TokenPosition token_pos = node->token_pos();
   if (node->field().is_const()) {
     ASSERT(node->field().StaticValue() != Object::sentinel().raw());
     ASSERT(node->field().StaticValue() !=
            Object::transition_sentinel().raw());
     Definition* result = new(Z) ConstantInstr(
         Instance::ZoneHandle(Z, node->field().StaticValue()), token_pos);
     return ReturnDefinition(result);
   }
-  Value* field_value = Bind(new(Z) ConstantInstr(node->field(), token_pos));
+  Value* field_value = Bind(new(Z) ConstantInstr(
+      Field::ZoneHandle(Z, node->field().Original()), token_pos));
   LoadStaticFieldInstr* load =
       new(Z) LoadStaticFieldInstr(field_value, token_pos);
   ReturnDefinition(load);
 }
 
 
 Definition* EffectGraphVisitor::BuildStoreStaticField(
     StoreStaticFieldNode* node,
     bool result_is_needed,
     TokenPosition token_pos) {
@@ skipping 902 matching lines @@
                    Script::Handle(function.script()),
                    function.token_pos(),
                    Report::AtLocation,
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart