- Update documentation of Dart_NewWeakPersistentHandle.

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 391 matching lines @@
  * Requires there to be a current isolate.
  */
 DART_EXPORT void Dart_DeletePersistentHandle(Dart_PersistentHandle object);
 
 /**
  * Allocates a weak persistent handle for an object.
  *
  * This handle has the lifetime of the current isolate unless it is
  * explicitly deallocated by calling Dart_DeletePersistentHandle.
  *
+ * If the object becomes unreachable the callback is invoked with the weak
+ * persistent handle and the peer as arguments. This gives the native code the
+ * ability to cleanup data associated with the object and to delete the weak
+ * persistent handle. It is illegal to call into the VM from the callback,
+ * except to delete the weak persistent handle.
+ *
  * Requires there to be a current isolate.
  *
  * \param object An object.
  * \param peer A pointer to a native object or NULL.  This value is
  *   provided to callback when it is invoked.
  * \param callback A function pointer that will be invoked sometime
  *   after the object is garbage collected.
  *
  * \return Success if the weak persistent handle was
  *   created. Otherwise, returns an error.
@@ skipping 1917 matching lines @@
  *
  * \param object An object.
  * \param peer A value to store in the peer field.
  *
  * \return Returns an error if 'object' is a subtype of Null, num, or
  *   bool.
  */
 DART_EXPORT Dart_Handle Dart_SetPeer(Dart_Handle object, void* peer);
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */