Build Observatory as part of runtime

runtime/observatory/test/dominator_tree_test.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.
 
 import 'package:observatory/dominator_tree.dart';
 import 'package:unittest/unittest.dart';
 
 void main() {
   test('small example from [Lenguaer & Tarjan 1979]', smallTest);
   test('non-flowgraph', nonFlowgraph);
@@ skipping 34 matching lines @@
   expect(d.dominator('J'), equals('G'));
   expect(d.dominator('L'), equals('D'));
   expect(d.dominator('R'), isNull);
 }
 
 void nonFlowgraph() {
   var d = new Dominator();
   d.addEdges('A', ['B']);
   expect(() => d.computeDominatorTree('B'), throwsStateError);
 }