Fix many warnings/errors when building Observatory

runtime/observatory/lib/src/models/objects/vm.dart

 // Copyright (c) 2016, 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 models;
 
 abstract class VMRef {
   /// A name identifying this vm. Not guaranteed to be unique.
   String get name;
 
   /// [Not actually from the apis]
   /// A name used to identify the VM in the UI.
   String get displayName;
 }
 
-abstract class VM implements VMRef {
+abstract class ServiceObjectOwner {
+  Future<dynamic> invokeRpc(String method, Map params);
+}
+
+abstract class VM implements VMRef, ServiceObjectOwner {
   /// Word length on target architecture (e.g. 32, 64).
   int get architectureBits;
 
   /// The CPU we are generating code for.
   String get targetCPU;
 
   /// The CPU we are actually running on.
   String get hostCPU;
 
   /// The Dart VM version string.
@@ skipping 14 matching lines @@
   int get maxRSS;
 
   /// The time that the VM started in milliseconds since the epoch.
   ///
   /// Suitable to pass to DateTime.fromMillisecondsSinceEpoch.
   DateTime get startTime;
 
   // A list of isolates running in the VM.
   Iterable<IsolateRef> get isolates;
 }