Use PassiveObject were possible.

runtime/vm/code_generator.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/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/bigint_operations.h"
 #include "vm/code_patcher.h"
@@ skipping 247 matching lines @@
 
 
 // Make a copy of the given context, including the values of the captured
 // variables.
 // Arg0: the context to be cloned.
 // Return value: newly allocated context.
 DEFINE_RUNTIME_ENTRY(CloneContext, 1) {
   const Context& ctx = Context::CheckedHandle(arguments.ArgAt(0));
   Context& cloned_ctx = Context::Handle(Context::New(ctx.num_variables()));
   cloned_ctx.set_parent(Context::Handle(ctx.parent()));
+  Instance& inst = Instance::Handle(isolate);
   for (int i = 0; i < ctx.num_variables(); i++) {
-    cloned_ctx.SetAt(i, Instance::Handle(ctx.At(i)));
+    inst = ctx.At(i);
+    cloned_ctx.SetAt(i, inst);
   }
   arguments.SetReturn(cloned_ctx);
 }
 
 
 // Helper routine for tracing a type check.
 static void PrintTypeCheck(
     const char* message,
     const Instance& instance,
     const AbstractType& type,
@@ skipping 1302 matching lines @@
   field.RecordStore(value);
 }
 
 
 DEFINE_RUNTIME_ENTRY(InitStaticField, 1) {
   const Field& field = Field::CheckedHandle(arguments.ArgAt(0));
   field.EvaluateInitializer();
 }
 
 }  // namespace dart