Teach the Observatory about WeakProperties (ephemerons).

runtime/bin/vmservice/observatory/lib/src/service/object.dart

Index: runtime/bin/vmservice/observatory/lib/src/service/object.dart
diff --git a/runtime/bin/vmservice/observatory/lib/src/service/object.dart b/runtime/bin/vmservice/observatory/lib/src/service/object.dart
index 8ed63c4354bba701984f36fa391ac925be8c25e9..18bbab4fd3a75c0ce65939ddf0bbf1615e9f9652 100644
--- a/runtime/bin/vmservice/observatory/lib/src/service/object.dart
+++ b/runtime/bin/vmservice/observatory/lib/src/service/object.dart
@@ -51,6 +51,7 @@ abstract class ServiceObject extends Observable {
   bool get isSentinel => vmType == 'Sentinel';
   bool get isString => vmType == 'String';
   bool get isType => vmType == 'Type';
+  bool get isWeakProperty => vmType == 'WeakProperty';
 
   /// The complete service url of this object.
   @reflectable String get link => _owner.relativeLink(_id);
@@ -122,6 +123,7 @@ abstract class ServiceObject extends Observable {
       case 'Smi':
       case 'String':
       case 'Type':
+      case 'WeakProperty':
         obj = new Instance._empty(owner);
         break;
       case 'Isolate':
@@ -1490,6 +1492,8 @@ class Instance extends ServiceObject {
   @observable var elements;
   @observable var userName;
   @observable var referent;  // If a MirrorReference.
+  @observable Instance key;  // If a WeakProperty.
+  @observable Instance value;  // If a WeakProperty.
 
   bool get isClosure => closureFunc != null;
 
@@ -1517,6 +1521,8 @@ class Instance extends ServiceObject {
     typeClass = map['type_class'];
     userName = map['user_name'];
     referent = map['referent'];
+    key = map['key'];
+    value = map['value'];
 
     // We are fully loaded.
     _loaded = true;