Get mus_ws_unittests working with Ozone X11.

testing/buildbot/chromium.chromiumos.json

 {
   "Linux ChromiumOS Builder": {
     "additional_compile_targets": [
       "All"
     ]
   },
   "Linux ChromiumOS Ozone Tests (1)": {
     "gtest_tests": [
       {
         "swarming": {
@@ skipping 230 matching lines @@
         "test": "mash_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "media_blink_unittests"
       },
       {
         "swarming": {
+          "can_use_on_swarming_builders": false
+        },
+        "test": "media_service_unittests"

[kylechar, 2017/02/02 18:01:29]

The media_service_unittests have been running on 'Mojo ChromiumOS' FYI trybot
for two months now. There are no failures on media_service_unittests in the
trybot history I can see, although it doesn't go back that far.

https://build.chromium.org/p/chromium.fyi/builders/Mojo%20ChromiumOS?numbuild...

+      },
+      {
+        "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "media_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "message_center_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "midi_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "mus_demo_unittests"
       },
       {
-        "args": [
-          "--ozone-platform=headless"

[sky, 2017/02/02 16:27:05]

How come this is no longer needed?

[kylechar, 2017/02/02 18:01:29]

This patch fixes mus_ws_unittests running with Ozone X11. This arg forced the
test to run with Ozone headless instead of Ozone X11 before, which is no longer
necessary.

-        ],
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "mus_ws_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "nacl_helper_nonsfi_unittests"
@@ skipping 852 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "wm_unittests"
       }
     ]
   }
 }