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

runtime/vm/dart_api_impl.h

 // Copyright (c) 2011, 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 VM_DART_API_IMPL_H_
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
 #include "vm/native_arguments.h"
 #include "vm/object.h"
@@ skipping 176 matching lines @@
     if (!raw->IsHeapObject()) {
       return kSmiCid;
     }
     return raw->GetClassId();
   }
 
   // Generates a handle used to designate an error return.
   static Dart_Handle NewError(const char* format, ...) PRINTF_ATTRIBUTE(1, 2);
 
   // Gets a handle to Null.
-  static Dart_Handle Null();
+  static Dart_Handle Null() {
+    return null_handle_;
+  }
 
   // Gets a handle to True.
-  static Dart_Handle True();
+  static Dart_Handle True() {
+    return true_handle_;
+  }
 
-  // Gets a handle to False
-  static Dart_Handle False();
+  // Gets a handle to False.
+  static Dart_Handle False() {
+    return false_handle_;
+  }
+
+  // Gets a handle to EmptyString.
+  static Dart_Handle EmptyString() {
+    return empty_string_handle_;
+  }
 
   // Retrieves the top ApiLocalScope.
   static ApiLocalScope* TopScope(Isolate* isolate);
 
   // Performs one-time initialization needed by the API.
   static void InitOnce();
 
   // Allocates handles for objects in the VM isolate.
   static void InitHandles();
 
@@ skipping 44 matching lines @@
 
  private:
   static Dart_Handle InitNewHandle(Isolate* isolate, RawObject* raw);
 
   // Thread local key used by the API. Currently holds the current
   // ApiNativeScope if any.
   static ThreadLocalKey api_native_key_;
   static Dart_Handle true_handle_;
   static Dart_Handle false_handle_;
   static Dart_Handle null_handle_;
+  static Dart_Handle empty_string_handle_;
 
   friend class ApiNativeScope;
 };
 
 class IsolateSaver {
  public:
   explicit IsolateSaver(Isolate* current_isolate)
       : saved_isolate_(current_isolate) {
   }
   ~IsolateSaver() {
@@ skipping 17 matching lines @@
   if (isolate->no_callback_scope_depth() != 0) {                               \
     return reinterpret_cast<Dart_Handle>(Api::AcquiredError(isolate));         \
   }                                                                            \
 
 #define ASSERT_CALLBACK_STATE(isolate)                                         \
   ASSERT(isolate->no_callback_scope_depth() == 0)
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_