- Add Dart_EmptyString to return the canonical empty string similar to how

runtime/vm/dart_api_impl_test.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 "bin/builtin.h"
 #include "include/dart_api.h"
 #include "include/dart_debugger_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
@@ skipping 502 matching lines @@
   Dart_Handle null = Dart_Null();
   EXPECT_VALID(null);
   EXPECT(Dart_IsNull(null));
 
   Dart_Handle str = NewString("test");
   EXPECT_VALID(str);
   EXPECT(!Dart_IsNull(str));
 }
 
 
+TEST_CASE(EmptyString) {
+  Dart_Handle empty = Dart_EmptyString();
+  EXPECT_VALID(empty);
+  EXPECT(!Dart_IsNull(empty));
+}
+
+
 TEST_CASE(IdentityEquals) {
   Dart_Handle five = Dart_NewInteger(5);
   Dart_Handle five_again = Dart_NewInteger(5);
   Dart_Handle mint = Dart_NewInteger(0xFFFFFFFF);
   Dart_Handle mint_again = Dart_NewInteger(0xFFFFFFFF);
   Dart_Handle abc = NewString("abc");
   Dart_Handle abc_again = NewString("abc");
   Dart_Handle xyz = NewString("abc");
   Dart_Handle dart_core = NewString("dart:core");
   Dart_Handle dart_mirrors = NewString("dart:mirrors");
@@ skipping 7875 matching lines @@
                                    NewString("main"),
                                    1,
                                    dart_args);
   int64_t value = 0;
   result = Dart_IntegerToInt64(result, &value);
   EXPECT_VALID(result);
   EXPECT_EQ(6, value);
 }
 
 }  // namespace dart