Convert sbox_validation_tests to run exclusively on Swarming

testing/buildbot/chromium.win.json

Index: testing/buildbot/chromium.win.json
diff --git a/testing/buildbot/chromium.win.json b/testing/buildbot/chromium.win.json
index 40fb0db72535a9f9bbf04f9a9ccf102d445d97a0..51f6c7e9c914b03225d633a55cf1e0f93b567a0c 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -229,6 +229,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -554,6 +557,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -1002,6 +1008,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -1307,6 +1316,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -1771,6 +1783,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {