Ensure objects emitted in code are allocated in old space.

runtime/vm/object_x64_test.cc

Index: runtime/vm/object_x64_test.cc
diff --git a/runtime/vm/object_x64_test.cc b/runtime/vm/object_x64_test.cc
index e1e64d203e897478fee4bc440415a9622e698121..74c0e5cd52920953101103c000ca730e59bcb510 100644
--- a/runtime/vm/object_x64_test.cc
+++ b/runtime/vm/object_x64_test.cc
@@ -32,7 +32,8 @@ void GenerateIncrement(Assembler* assembler) {
 // Generate a dart code sequence that embeds a string object in it.
 // This is used to test Embedded String objects in the instructions.
 void GenerateEmbedStringInCode(Assembler* assembler, const char* str) {
-  const String& string_object = String::ZoneHandle(String::New(str));
+  const String& string_object =
+      String::ZoneHandle(String::New(str, Heap::kOld));
   __ LoadObject(RAX, string_object);
   __ ret();
 }