Fix many warnings/errors when building Observatory

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

Index: runtime/observatory/lib/src/models/objects/vm.dart
diff --git a/runtime/observatory/lib/src/models/objects/vm.dart b/runtime/observatory/lib/src/models/objects/vm.dart
index 05e1bba8531ba410fac08903511156672273b0b0..f1f50885943e406fe82fa71a6b5fb5465e36e42b 100644
--- a/runtime/observatory/lib/src/models/objects/vm.dart
+++ b/runtime/observatory/lib/src/models/objects/vm.dart
@@ -13,7 +13,11 @@ abstract class VMRef {
   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;