Rename "service_unittests" -> "services_unittests".

testing/buildbot/chromium.mac.json

Index: testing/buildbot/chromium.mac.json
diff --git a/testing/buildbot/chromium.mac.json b/testing/buildbot/chromium.mac.json
index dd3f7cb7ec125f524c53d52169b60d72a82df57f..2773bb806fc12bb94331f6466fb5b19c898800c4 100644
--- a/testing/buildbot/chromium.mac.json
+++ b/testing/buildbot/chromium.mac.json
@@ -337,7 +337,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -771,7 +771,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -1225,7 +1225,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -1643,7 +1643,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {
@@ -2042,7 +2042,7 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
-        "test": "service_unittests"
+        "test": "services_unittests"
       },
       {
         "swarming": {