Use a tag bit for indicating prologue weak persistent handles, this avoids

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 111 matching lines @@
                                           Dart_Handle object);
   CLASS_LIST_FOR_HANDLES(DECLARE_UNWRAP)
 #undef DECLARE_UNWRAP
 
   // Unwraps the raw object from the handle using a reused handle.
   static const String& UnwrapStringHandle(
       const ReusableObjectHandleScope& reused, Dart_Handle object);
   static const Instance& UnwrapInstanceHandle(
       const ReusableObjectHandleScope& reused, Dart_Handle object);
 
-  // Validates and converts the passed in handle as a persistent handle.
-  static PersistentHandle* UnwrapAsPersistentHandle(
-      Dart_PersistentHandle object);
-
-  // Validates and converts the passed in handle as a weak persistent handle.
-  static FinalizablePersistentHandle* UnwrapAsWeakPersistentHandle(
-      Dart_WeakPersistentHandle object);
-
-  // Validates and converts the passed in handle as a prologue weak
-  // persistent handle.
-  static FinalizablePersistentHandle* UnwrapAsPrologueWeakPersistentHandle(
-      Dart_WeakPersistentHandle object);
-
   // Returns an Error handle if isolate is in an inconsistent state.
   // Returns a Success handle when no error condition exists.
   static Dart_Handle CheckIsolateState(Isolate *isolate);
 
   // Casts the internal Isolate* type to the external Dart_Isolate type.
   static Dart_Isolate CastIsolate(Isolate* isolate);
 
   // Gets the handle used to designate successful return.
   static Dart_Handle Success() { return Api::True(); }
 
@@ skipping 124 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_