Implement weak persistent handles in the Dart API.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index ea89dd0d9ac278d829621915ec82392f84eb5f88..89f270d9594d2419fd8eb662b47d871c0f5cb18d 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -204,24 +204,21 @@ DART_EXPORT Dart_Handle Dart_NewPersistentHandle(Dart_Handle object);
 DART_EXPORT void Dart_DeletePersistentHandle(Dart_Handle object);
 
 /**
- * Takes a persistent handle and makes it weak.
+ * Allocates a weak persistent handle for an object.
  *
- * UNIMPLEMENTED.
+ * This handle has the lifetime of the current isolate unless it is
+ * explicitly deallocated by calling Dart_DeletePersistentHandle.
  *
  * Requires there to be a current isolate.
  */
-DART_EXPORT Dart_Handle Dart_MakeWeakPersistentHandle(Dart_Handle object);
-// TODO(turnidge): Needs a "near death" callback here.
-// TODO(turnidge): Add IsWeak, Clear, etc.
+DART_EXPORT Dart_Handle Dart_NewWeakPersistentHandle(Dart_Handle object);
 
 /**
- * Takes a weak persistent handle and makes it non-weak.
- *
- * UNIMPLEMENTED.
+ * Is this object a weak persistent handle?
  *
  * Requires there to be a current isolate.
  */
-DART_EXPORT Dart_Handle Dart_MakePersistentHandle(Dart_Handle object);
+DART_EXPORT bool Dart_IsWeakPersistentHandle(Dart_Handle object);
 
 // --- Initialization and Globals ---