Switch mash_browser_tests to Ozone X11 platform.

testing/buildbot/chromium.chromiumos.json

 {
   "Linux ChromiumOS Builder": {
     "additional_compile_targets": [
       "All"
     ]
   },
   "Linux ChromiumOS Ozone Tests (1)": {
     "gtest_tests": [
       {
         "swarming": {
@@ skipping 46 matching lines @@
         },
         "test": "aura_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "base_unittests"
       },
       {
-        "args": [
-          "--ozone-platform=headless",
-          "--override-use-gl-with-osmesa-for-tests",
-          "--run-in-mash",
-          "--service-overrides=src/chrome/app/mash/mash_service_overrides.json",
-          "--test-launcher-filter-file=src/testing/buildbot/filters/mash.browser_tests.filter",
-          "--use-test-config"
-        ],
-        "hard_timeout": 60,
-        "name": "mash_browser_tests",
-        "swarming": {
-          "can_use_on_swarming_builders": false
-        },
-        "test": "browser_tests"
-      },
-      {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "cacheinvalidation_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "capture_unittests"
@@ skipping 135 matching lines @@
         },
         "test": "ipc_tests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "jingle_unittests"
       },
       {
+        "args": [
+          "--test-launcher-filter-file=../../testing/buildbot/filters/mash.browser_tests.filter"
+        ],
+        "hard_timeout": 60,
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "mash_browser_tests"
+      },
+      {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "mash_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "media_blink_unittests"
@@ skipping 894 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "wm_unittests"
       }
     ]
   }
 }