buildbot: Enable swarming on chromium_linux_ng.

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 3250 matching lines @@
         }
       },
       {
         "isolate_name": "devtools_eslint",
         "name": "devtools_eslint",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
+        "isolate_name": "webkit_layout_tests_exparchive",
+        "name": "webkit_layout_tests_exparchive",
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "shards": 1
+        }
+      },
+      {
         "isolate_name": "telemetry_gpu_unittests",
         "name": "telemetry_gpu_unittests",
         "override_compile_targets": [
           "telemetry_gpu_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
@@ skipping 968 matching lines @@
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 4
         }
       }
     ]
   }
 }