Add cast_accessibility_unittests to "Cast Linux" bots

Bug: 1152873
Test: CQ
Change-Id: Ib7bb8a862e8e72862a01d1e2087b567e09ddf3cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560812Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832107}

testing/buildbot/chromium.linux.json

@@ -1106,6 +1106,23 @@
         "test": "capture_unittests",
         "test_id_prefix": "ninja://media/capture:capture_unittests/"
       },
+      {
+        "merge": {
+          "args": [],
+          "script": "//testing/merge_scripts/standard_gtest_merge.py"
+        },
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "dimension_sets": [
+            {
+              "os": "Ubuntu-16.04"
+            }
+          ],
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
+        },
+        "test": "cast_accessibility_unittests",
+        "test_id_prefix": "ninja://chromecast/browser/accessibility/flutter:cast_accessibility_unittests/"
+      },
       {
         "merge": {
           "args": [],

testing/buildbot/gn_isolate_map.pyl

@@ -341,6 +341,10 @@
     "label": "//media/capture:capture_unittests",
     "type": "windowed_test_launcher",
   },
+  "cast_accessibility_unittests": {
+    "label": "//chromecast/browser/accessibility/flutter:cast_accessibility_unittests",
+    "type": "console_test_launcher",
+  },
   "cast_runner_browsertests": {
     "label": "//fuchsia/runners:cast_runner_browsertests",
     "type": "console_test_launcher",

testing/buildbot/test_suites.pyl

@@ -403,6 +403,7 @@
     },
 
     'cast_video_specific_chromium_gtests': {
+      'cast_accessibility_unittests': {},
       'cast_graphics_unittests': {},
       'exo_unittests': {},
       'views_unittests': {