Converted accessibility_unittests to run on Swarming everywhere.

testing/buildbot/chromium.linux.json

 {
   "Android Tests": {
     "scripts": [
       {
         "name": "webview_licenses",
         "script": "webview_licenses.py"
       }
     ]
   },
   "Android Tests (dbg)": {
     "scripts": [
       {
         "name": "webview_licenses",
         "script": "webview_licenses.py"
       }
     ]
   },
   "Linux Clang (dbg)": {
     "gtest_tests": [
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "accessibility_unittests"
       },
       {
         "test": "app_shell_unittests"
       },
       {
         "test": "base_unittests"
       },
       {
         "test": "components_unittests"
@@ skipping 797 matching lines @@
       }
     ],
     "scripts": [
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
       }
     ]
   }
 }