Convert url_unittests 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 e0e2e5c69ae7bb0cf7a49fa06cf82435feb77d8c..f4b0c336425a8cb726448e8f66ee9fbb4a06ff65 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -229,6 +229,9 @@
         "test": "unit_tests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "url_unittests"
       },
       {
@@ -500,6 +503,9 @@
         "test": "unit_tests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "url_unittests"
       },
       {
@@ -890,6 +896,9 @@
         "test": "unit_tests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "url_unittests"
       },
       {
@@ -1141,6 +1150,9 @@
         "test": "unit_tests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "url_unittests"
       },
       {
@@ -1549,6 +1561,9 @@
         "test": "unit_tests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "url_unittests"
       },
       {