Respond to Ivan's code review comments from previous TBR cl.

runtime/vm/object_test.cc

Index: runtime/vm/object_test.cc
diff --git a/runtime/vm/object_test.cc b/runtime/vm/object_test.cc
index 4cfee0b913c5f870798c09ff1462fb58a313e599..cba6d447f027c74ffb5fa31aaf5d0455237a0440 100644
--- a/runtime/vm/object_test.cc
+++ b/runtime/vm/object_test.cc
@@ -1544,11 +1544,8 @@ TEST_CASE(EscapeSpecialCharactersOneByteString) {
       String::Handle(String::EscapeSpecialCharacters(str));
   EXPECT(escaped_str.Equals("a\\n\\f\\b\\t\\v\\r\\\\\\$z"));
 
-  const String& empty_str = String::Handle(
-      OneByteString::New(static_cast<intptr_t>(0), Heap::kNew));
   const String& escaped_empty_str =
-      String::Handle(String::EscapeSpecialCharacters(empty_str));
-  EXPECT_EQ(empty_str.Length(), 0);
+      String::Handle(String::EscapeSpecialCharacters(Symbols::Empty()));
   EXPECT_EQ(escaped_empty_str.Length(), 0);
 }