Add switch to mash's browser_tests

testing/buildbot/chromium.mojo.json

 {
   "Chromium Mojo Android": {
     "additional_compile_targets": [
       "mash:all"
     ],
     "scripts": [
       {
         "name": "mojo_apptests",
         "script": "mojo_apptests.py"
       }
@@ skipping 27 matching lines @@
       }
     ]
   },
   "Chromium Mojo Windows": {
     "additional_compile_targets": [
       "mash:all"
     ],
     "gtest_tests": [
       {
         "args": [
+          "--override-use-gl-with-osmesa-for-tests",
           "--run-in-mash",
           "--test-launcher-filter-file=src/testing/buildbot/filters/mojo.fyi.browser_tests.filter"
         ],
         "test": "browser_tests"
       },
       {
         "test": "mus_ws_unittests"
       },
       {
         "test": "views_mus_unittests"
       }
     ],
     "scripts": [
       {
         "name": "mojo_apptests",
         "script": "mojo_apptests.py"
       }
     ]
   }
 }