Run mus_demo_unittests on X11 Chrome OS trybot.

Run mus_demo_unittests on the X11 Chrome OS trybot. This test just
checks that mojo:mus_demo starts and draws a frame. When tcmalloc
problems are fixed this should run on Ozone Chrome OS trybot (ideally
with Ozone X11).

BUG=611473

Review-Url: https://codereview.chromium.org/2151093003
Cr-Commit-Position: refs/heads/master@{#419226}

services/ui/demo/BUILD.gn

@@ -62,6 +62,7 @@ test("mus_demo_unittests") {
   ]
 
   data_deps = [
+    ":mus_demo",
     ":test_manifest",
   ]
 }

testing/buildbot/chromium.chromiumos.json

@@ -671,6 +671,12 @@
         },
         "test": "midi_unittests"
       },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "mus_demo_unittests"
+      },
       {
         "swarming": {
           "can_use_on_swarming_builders": true

testing/buildbot/gn_isolate_map.pyl

@@ -500,6 +500,10 @@
     "label": "//services/ui/gpu:mus_gpu_unittests",
     "type": "console_test_launcher",
   },
+  "mus_demo_unittests": {
+    "label": "//services/ui/demo:mus_demo_unittests",
+    "type": "windowed_test_launcher",
+  },
   "mus_ws_unittests": {
     "label": "//services/ui/ws:mus_ws_unittests",
     "type": "windowed_test_launcher",