Enabled wm_unittests on Windows builders

testing/buildbot/chromium_trybot.json

 {
   "compile_targets": [
     "all"
   ],
   "gtest_tests": [
     "accessibility_unittests",
     "app_list_unittests",
     {
       "test": "ash_unittests",
       "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"],
@@ skipping 148 matching lines @@
     {
       "test": "unit_tests",
       "swarming": {
         "can_use_on_swarming_builders": true,
         "shards": 2
       }
     },
     "url_unittests",
     {
       "test": "wm_unittests",
-      "platforms": ["linux"]
+      "platforms": ["linux", "win"]
     },
     {
       "test": "app_shell_browsertests",
       "platforms": ["linux"]
     },
     {
       "test": "app_shell_unittests",
       "platforms": ["linux", "win"]
     },
     {
@@ skipping 44 matching lines @@
   "non_filter_tests_builders": [
   ],
 
   "filter_compile_builders": [
     "win_chromium_compile_dbg",
     "win_chromium_rel_swarming",
     "win_chromium_x64_rel_swarming",
     "win8_chromium_rel"
   ]
 }