Speculative Fix for missing test filter

The Mojo Windows bot cannot find the test filter. This change updates the path
to be more specific. Like that of the Cast Linux testing filter

TEST=viz_content_browsertest

Bug: 760181
Change-Id: Ib2516b5c0dd5513b4acf56f8083e5bd47fe7719f
Reviewed-on: https://chromium-review.googlesource.com/822659Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523828}

testing/buildbot/chromium.fyi.json

@@ -4428,25 +4428,26 @@
         ],
         "name": "viz_content_browsertests",
         "swarming": {
-          "can_use_on_swarming_builders": false
+          "can_use_on_swarming_builders": true,
+          "shards": 2
         },
         "test": "content_browsertests"
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": false
+          "can_use_on_swarming_builders": true
         },
         "test": "media_service_unittests"
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": false
+          "can_use_on_swarming_builders": true
         },
         "test": "services_unittests"
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": false
+          "can_use_on_swarming_builders": true
         },
         "test": "views_mus_interactive_ui_tests"
       }

testing/buildbot/waterfalls.pyl

@@ -1138,7 +1138,6 @@
         'test_suites': {
           'gtest_tests': 'mojo_windows_gtests',
         },
-        'use_swarming': False,
       },
       'Out of Process Profiling Android': {
         'swarming': {