Fixing contexts_tests service test in checked mode

runtime/observatory/lib/src/service/object.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.
 
 part of service;
 
 // Some value smaller than the object ring, so requesting a large array
 // doesn't result in an expired ref because the elements lapped it in the
 // object ring.
 const int kDefaultFieldLimit = 100;
@@ skipping 2774 matching lines @@
     // We are fully loaded.
     _loaded = true;
   }
 
   String toString() => 'Context($length)';
 }
 
 class ContextElement extends M.ContextElement {
   final Guarded<Instance> value;
 
-  ContextElement(ServiceMap map)
+  ContextElement(ObservableMap map)
     : value = new Guarded<Instance>(map['value']);
 }
 
 M.FunctionKind stringToFunctionKind(String value) {
   switch(value) {
     case 'RegularFunction': return M.FunctionKind.regular;
     case 'ClosureFunction': return M.FunctionKind.closure;
     case 'GetterFunction': return M.FunctionKind.getter;
     case 'SetterFunction': return M.FunctionKind.setter;
     case 'Constructor': return M.FunctionKind.constructor;
@@ skipping 1489 matching lines @@
     var v = list[i];
     if ((v is ObservableMap) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is ObservableList) {
       _upgradeObservableList(v, owner);
     } else if (v is ObservableMap) {
       _upgradeObservableMap(v, owner);
     }
   }
 }