observatory: populate 'architecture' in VM, and add numerical vmId in Class.

runtime/bin/vmservice/observatory/test/vm_test.dart

Index: runtime/bin/vmservice/observatory/test/vm_test.dart
===================================================================
--- runtime/bin/vmservice/observatory/test/vm_test.dart	(revision 0)
+++ runtime/bin/vmservice/observatory/test/vm_test.dart	(working copy)
@@ -0,0 +1,16 @@
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+
+var tests = [
+
+(Isolate isolate) {
+  VM vm = isolate.owner;
+  expect(vm.targetCPU, isNotNull);
+  expect(vm.architectureBits == 32 ||
+         vm.architectureBits == 64, isTrue);
+},
+
+];
+
+main(args) => runIsolateTests(args, tests);