Add a weak property type to the virtual machine.

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 5392 matching lines @@
     // This is only safe because we create a new Smi, which does not cause
     // heap allocation.
     raw_ptr()->data_length_ = Smi::New(value);
   }
 
   HEAP_OBJECT_IMPLEMENTATION(JSRegExp, Instance);
   friend class Class;
 };
 
 
+class WeakProperty : public Instance {
+ public:
+  RawObject* key() const {
+    return raw_ptr()->key_;
+  }
+
+  void set_key(const Object& key) {
+    StorePointer(&raw_ptr()->key_, key.raw());
+  }
+
+  RawObject* value() const {
+    return raw_ptr()->value_;
+  }
+
+  void set_value(const Object& value) {
+    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) {
+    raw_weak->ptr()->key_ = Object::null();
+    raw_weak->ptr()->value_ = Object::null();
+  }
+
+ private:
+  HEAP_OBJECT_IMPLEMENTATION(WeakProperty, Instance);
+  friend class Class;
+};
+
+
 // Breaking cycles and loops.
 RawClass* Object::clazz() const {
   uword raw_value = reinterpret_cast<uword>(raw_);
   if ((raw_value & kSmiTagMask) == kSmiTag) {
     return Smi::Class();
   }
   return Isolate::Current()->class_table()->At(raw()->GetClassId());
 }
 
 
@@ skipping 91 matching lines @@
     if (this->CharAt(i) != str.CharAt(begin_index + i)) {
       return false;
     }
   }
   return true;
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_