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

runtime/include/dart_api.h

 /*
  * 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.
  */
 
 #ifndef INCLUDE_DART_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
@@ skipping 1244 matching lines @@
 
 /*
  * =======
  * Objects
  * =======
  */
 
 /**
  * Returns the null object.
  *
- * Requires there to be a current isolate.
- *
  * \return A handle to the null object.
  */
 DART_EXPORT Dart_Handle Dart_Null();
 
 /**
+ * Returns the empty string object.
+ *
+ * \return A handle to the empty string object.
+ */
+DART_EXPORT Dart_Handle Dart_EmptyString();
+
+/**
  * Is this object null?
  */
 DART_EXPORT bool Dart_IsNull(Dart_Handle object);
 
 /**
  * Checks if the two objects are equal.
  *
  * The result of the comparison is returned through the 'equal'
  * parameter. The return value itself is used to indicate success or
  * failure, not equality.
@@ skipping 1442 matching lines @@
  * NOTE: If multiple callbacks with the same name are registered, only the
  * last callback registered will be remembered.
  */
 DART_EXPORT void Dart_RegisterRootServiceRequestCallback(
     const char* name,
     Dart_ServiceRequestCallback callback,
     void* user_data);
 
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */