Added new implementations for virtual containers

runtime/observatory/observatory_sources.gypi

 # Copyright (c) 2015, 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.
 
 # This file contains all dart, css, and html sources for Observatory.
 {
   'sources': [
     'lib/app.dart',
     'lib/cli.dart',
     'lib/cpu_profile.dart',
@@ skipping 28 matching lines @@
     'lib/src/elements/class_view.dart',
     'lib/src/elements/class_view.html',
     'lib/src/elements/code_ref.dart',
     'lib/src/elements/code_ref.html',
     'lib/src/elements/code_view.dart',
     'lib/src/elements/code_view.html',
     'lib/src/elements/context_ref.dart',
     'lib/src/elements/context_ref.html',
     'lib/src/elements/context_view.dart',
     'lib/src/elements/context_view.html',
+    'lib/src/elements/containers/virtual_collection.dart',
+    'lib/src/elements/containers/virtual_tree.dart',
     'lib/src/elements/cpu_profile.dart',
     'lib/src/elements/cpu_profile.html',
     'lib/src/elements/css/shared.css',
     'lib/src/elements/curly_block.dart',
     'lib/src/elements/curly_block_wrapper.dart',
     'lib/src/elements/debugger.dart',
     'lib/src/elements/debugger.html',
     'lib/src/elements/error_ref.dart',
     'lib/src/elements/error_ref.html',
     'lib/src/elements/error_view.dart',
@@ skipping 155 matching lines @@
     'lib/utils.dart',
     'web/favicon.ico',
     'web/index.html',
     'web/main.dart',
     'web/third_party/trace_viewer_full.html',
     'web/timeline.html',
     'web/timeline.js',
     'web/timeline_message_handler.js',
   ],
 }