Add sandbox_mac_unittests to the chromium.mac and chromium_trybot recipes.

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 e095afe6e85d34814c5cce91e2eb7923fd7d1cf7..bb4b7a4a7c3b36307ebf187e7c14ab2a183d5a13 100644
--- a/testing/buildbot/chromium.mac.json
+++ b/testing/buildbot/chromium.mac.json
@@ -49,6 +49,7 @@
       "mojo_public_utility_unittests",
       "mojo_service_manager_unittests",
       "mojo_system_unittests",
+      "sandbox_mac_unittests",
       {"test": "browser_tests", "shard_index": 2, "total_shards": 3}
     ]
   },
@@ -102,6 +103,7 @@
       "mojo_public_utility_unittests",
       "mojo_service_manager_unittests",
       "mojo_system_unittests",
+      "sandbox_mac_unittests",
       {"test": "browser_tests", "shard_index": 2, "total_shards": 3}
     ]
   },
@@ -128,6 +130,7 @@
       "gfx_unittests",
       "media_unittests",
       "net_unittests",
+      "sandbox_mac_unittests",
       {"test": "browser_tests", "shard_index": 1, "total_shards": 4}
     ]
   },
@@ -185,6 +188,7 @@
       "gfx_unittests",
       "media_unittests",
       "net_unittests",
+      "sandbox_mac_unittests",
       {"test": "browser_tests", "shard_index": 1, "total_shards": 4}
     ]
   },