Add request tracing to Observatory:

runtime/bin/vmservice/client/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;
 
 /// A [ServiceObject] is an object known to the VM service and is tied
 /// to an owning [Isolate].
 abstract class ServiceObject extends Observable {
   static int LexicalSortName(ServiceObject o1, ServiceObject o2) {
@@ skipping 398 matching lines @@
     })));
   }
 
   /// Gets [id] as an [ObservableMap] from the service directly. If
   /// an error occurs, the future is completed as an error with a
   /// ServiceError or ServiceException. Therefore any chained then() calls
   /// will only receive a map encoding a valid ServiceObject.
   Future<ObservableMap> getAsMap(String id) {
     return getString(id).then((response) {
       var map = _parseJSON(response);
+      if (Tracer.current != null) {
+        Tracer.current.trace("Received response for ${id}", map:map);
+      }
       return _processMap(map);
     }).catchError((error) {
       // ServiceError, forward to VM's ServiceError stream.
       errors.add(error);
       return new Future.error(error);
     }, test: (e) => e is ServiceError).catchError((exception) {
       // ServiceException, forward to VM's ServiceException stream.
       exceptions.add(exception);
       return new Future.error(exception);
     }, test: (e) => e is ServiceException);
@@ skipping 1804 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);
     }
   }
 }