Convert Mojo tests to use 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 d974baaf26acf2eb9c7fdb2e7ac2627479261fc9..ffc6501ca67e638983567d311a50ba46f99aa148 100644
--- a/testing/buildbot/chromium.win.json
+++ b/testing/buildbot/chromium.win.json
@@ -265,6 +265,9 @@
         "test": "mojo_public_system_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mojo_system_unittests"
       },
       {
@@ -690,6 +693,9 @@
         "test": "mojo_public_system_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mojo_system_unittests"
       },
       {
@@ -1124,6 +1130,9 @@
         "test": "mojo_public_system_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mojo_system_unittests"
       },
       {
@@ -1561,6 +1570,9 @@
         "test": "mojo_public_system_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mojo_system_unittests"
       },
       {
@@ -1933,6 +1945,9 @@
         "test": "mojo_public_system_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "mojo_system_unittests"
       },
       {