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 0ae1d2c36e7d75ec3bbc9cec9058c44c8ff1692a..a45cbb3c98f8e0217480bac14ef8defefdef6907 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"
       },
       {
@@ -998,6 +1004,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -1296,6 +1305,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {
@@ -1756,6 +1768,9 @@
         "test": "sbox_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sbox_validation_tests"
       },
       {