Rename "service_unittests" -> "services_unittests".

testing/buildbot/chromium.linux.json

Index: testing/buildbot/chromium.linux.json
diff --git a/testing/buildbot/chromium.linux.json b/testing/buildbot/chromium.linux.json
index af13fbea83afafe9b0bb9ad6b7cdc06a12e3cbcd..e9c3b380c0531d7da562488955dfece5dfdc9f1a 100644
--- a/testing/buildbot/chromium.linux.json
+++ b/testing/buildbot/chromium.linux.json
@@ -2806,7 +2806,7 @@
             }
           ]
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "merge": {
@@ -4019,7 +4019,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -4674,7 +4674,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -5083,7 +5083,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {