Refactor the dart api a bit:

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"
 
-#define RETURN_FAILURE(msg) return Dart_ErrorResult(msg)
-#define RETURN_CINT(retval) return Dart_ResultAsCIntptr(retval)
-#define RETURN_CBOOLEAN(retval) return Dart_ResultAsCBoolean(retval)
-#define RETURN_CSTRING(retval) return Dart_ResultAsCString(retval)
-#define RETURN_OBJECT(obj) return Dart_ResultAsObject(Api::NewLocalHandle(obj))
-#define RETURN_CINT64(retval) return Dart_ResultAsCInt64(retval)
-#define RETURN_CDOUBLE(retval) return Dart_ResultAsCDouble(retval)
-
 namespace dart {
 
-// Forward declarations.
+class ApiState;
+class LocalHandle;
 class Object;
+class PersistentHandle;
 class RawObject;
-class LocalHandle;
-class PersistentHandle;
-class ApiState;
 
 class Api : AllStatic {
  public:
   // Create new local handles.
   static Dart_Handle NewLocalHandle(const Object& object);
 
   // Unwrap the raw object from the handle.
   static RawObject* UnwrapHandle(Dart_Handle object);
 
   // Validate and convert the passed in handle as a local handle.
   static LocalHandle* UnwrapAsLocalHandle(const ApiState& state,
                                           Dart_Handle object);
 
   // Validate and convert the passed in handle as a persistent handle.
   static PersistentHandle* UnwrapAsPersistentHandle(const ApiState& state,
                                                     Dart_Handle object);
 
+  // Get the handle used to designate successful return.
+  static Dart_Handle Success();
+
+  // Generate a handle used to designate an error return.
+  static Dart_Handle Error(const char* msg);
+
   // Allocate space in the local zone.
   static uword Allocate(intptr_t size);
 
   // Reallocate space in the local zone.
   static uword Reallocate(uword ptr, intptr_t old_size, intptr_t new_size);
 };
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_