Add libjingle_xmpp_unittests to Chromium bots.

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 643a90a82994d8fed038410587aba2e73f5af464..d5231b9e4279d0d9997c5c2fe683bee7e064002e 100644
--- a/testing/buildbot/chromium.mac.json
+++ b/testing/buildbot/chromium.mac.json
@@ -217,6 +217,12 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "libjingle_xmpp_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mac_installer_unittests"
       },
       {
@@ -642,6 +648,12 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "libjingle_xmpp_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mac_installer_unittests"
       },
       {
@@ -1017,6 +1029,12 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "libjingle_xmpp_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mac_installer_unittests"
       },
       {
@@ -1370,6 +1388,12 @@
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "libjingle_xmpp_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mac_installer_unittests"
       },
       {