Use the return value of vm native methods to set the return value,

vm/native_entry_test.cc

Index: vm/native_entry_test.cc
===================================================================
--- vm/native_entry_test.cc	(revision 11327)
+++ vm/native_entry_test.cc	(working copy)
@@ -51,7 +51,7 @@
   const Smi& right = Smi::CheckedHandle(arguments->At(1));
   // Ignoring overflow in the calculation below.
   intptr_t result = left.Value() - right.Value();
-  arguments->SetReturn(Smi::Handle(Smi::New(result)));
+  return Smi::New(result);
 }
 
 
@@ -65,7 +65,7 @@
     // Ignoring overflow in the addition below.
     result += arg.Value();
   }
-  arguments->SetReturn(Smi::Handle(Smi::New(result)));
+  return Smi::New(result);
 }
 
 
@@ -84,6 +84,7 @@
   const uword function_entry_address =
       Code::Handle(target_function.CurrentCode()).EntryPoint();
   EXPECT_EQ(function_entry_address, target_address);
+  return Object::null();
 }
 
 }  // namespace dart