Teach the Observatory about WeakProperties (ephemerons).

runtime/bin/vmservice/observatory/test/weak_properties_test.dart

+// Copyright (c) 2014, 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.
+
+library vm_references_test;
+
+import 'dart:async';
+import 'dart:mirrors';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+
+class Foo { }
+class Bar { }
+
+var expando;
+var key;
+var value;
+var weak_property;
+
+void script() {
+  expando = new Expando('some debug name');
+  key = new Foo();
+  value = new Bar();
+  expando[key] = value;
+
+  InstanceMirror expandoMirror = reflect(expando);
+  LibraryMirror libcore = expandoMirror.type.owner;
+
+  var entries = expandoMirror.getField(MirrorSystem.getSymbol('_data', libcore)).reflectee;
+  weak_property = entries.singleWhere((e) => e != null);
+  print(weak_property);
+}
+
+var tests = [
+
+(Isolate isolate) =>
+  isolate.rootLib.load().then((Library lib) {
+    ServiceMap keyField = lib.variables.singleWhere((v) => v.name == 'key');
+    Instance key = keyField['value'];
+    ServiceMap valueField = lib.variables.singleWhere((v) => v.name == 'value');
+    Instance value = valueField['value'];
+    ServiceMap propField = lib.variables.singleWhere((v) => v.name == 'weak_property');
+    Instance prop = propField['value'];
+
+    expect(key.isWeakProperty, isFalse);
+    expect(value.isWeakProperty, isFalse);
+    expect(prop.isWeakProperty, isTrue);
+    expect(prop.key, isNull);
+    expect(prop.value, isNull);
+    return prop.load().then((Instance loadedProp) {
+      // Object ids are not cannonicalized, so we rely on the key and value
+      // being the sole instances of their classes to test we got the objects
+      // we expect.
+      expect(loadedProp.key, isNotNull);
+      expect(loadedProp.key.clazz, equals(key.clazz));
+      expect(loadedProp.value, isNotNull);
+      expect(loadedProp.value.clazz, equals(value.clazz));
+    });
+  }),
+
+];
+
+main(args) => runIsolateTests(args, tests, testeeBefore: script);