Add Observatory mojo_shell hearbeat test

mojo/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//build/module_args/mojo.gni")
 import("//mojo/public/mojo.gni")
 
 # TODO(beng): this meta target should probably move to the root dir's BUILD.gn.
 group("mojo") {
   # Meta-target, don't link into production code.
   testonly = true
   declare_args() {
     mojo_use_go = false
 
     # TODO(ncbray): support ASAN once NaCl's GN build is unforked.
     mojo_use_nacl = is_linux && !is_asan
   }
   deps = [
     ":tests",
     "//benchmarks",
     "//examples",
     "//mojo/common",
     "//mojo/dart/apptest",
     "//mojo/dart/apptest:apptest_pkg",
     "//mojo/dart/mojom",
     "//mojo/dart/mojo_services",
+    "//mojo/dart/observatory_test",
     "//mojo/public",
     "//mojo/services",
     "//services",
   ]
 
   if (is_android) {
     deps += [
       "//mojo/android",
       "//mojo/tools/android_shortcuts",
       "//mojo/tools:remote_file_reader",
@@ skipping 61 matching lines @@
       "//mojo/edk/js:tests",
       "//services/js:js_apptests",
       "//services/js:js_services_unittests",
     ]
   }
 
   if (mojo_use_prebuilt_network_service) {
     deps += [ "//mojo/public/tools:copy_network_service_apptests" ]
   }
 }