Expose the WeakProperty type.

runtime/vm/object.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 VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 5398 matching lines @@
   friend class Class;
 };
 
 
 class WeakProperty : public Instance {
  public:
   RawObject* key() const {
     return raw_ptr()->key_;
   }
 
-  void set_key(const Object& key) {
+  void set_key(const Object& key) const {
     StorePointer(&raw_ptr()->key_, key.raw());
   }
 
   RawObject* value() const {
     return raw_ptr()->value_;
   }
 
-  void set_value(const Object& value) {
+  void set_value(const Object& value) const {
     StorePointer(&raw_ptr()->value_, value.raw());
   }
 
   static RawWeakProperty* New(Heap::Space space = Heap::kNew);
 
   static intptr_t InstanceSize() {
     return RoundedAllocationSize(sizeof(RawWeakProperty));
   }
 
   static void Clear(RawWeakProperty* raw_weak) {
@@ skipping 111 matching lines @@
     if (this->CharAt(i) != str.CharAt(begin_index + i)) {
       return false;
     }
   }
   return true;
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_