Add mojo unittests to Windows main waterfall bots.

testing/buildbot/chromium_trybot.json

 {
   "gtest_tests": [
     "accessibility_unittests",
     "app_list_unittests",
     "base_unittests",
     {
       "test": "browser_tests",
       "exclude_builders": ["tryserver.chromium:win_chromium_x64_rel"]
     },
     "cacheinvalidation_unittests",
@@ skipping 54 matching lines @@
     {
       "test": "ash_unittests",
       "platforms": ["win"]
     },
     {
       "test": "aura_unittests",
       "platforms": ["linux", "win"]
     },
     {
       "test": "mojo_view_manager_unittests",
-      "platforms": ["linux"]
+      "platforms": ["linux", "win"]
     },
     {
       "test": "sandbox_linux_unittests",
       "platforms": ["linux"],
       "args": ["--test-launcher-print-test-stdio=always"]
     },
     {
       "test": "sandbox_mac_unittests",
       "platforms": ["mac"]
     },
@@ skipping 26 matching lines @@
       "platforms": ["linux"],
       "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"]
     },
     {
       "test": "wm_unittests",
       "platforms": ["linux"],
       "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"]
     }
   ]
 }