Fix low risk nullable => non nullable change for NavigatorLanguage.language

third_party/WebKit/LayoutTests/imported/wpt/MANIFEST.json

 {
   "items": {
     "manual": [],
     "reftest": [],
     "stub": [],
     "testharness": [],
     "wdspec": []
   },
   "local_changes": {
     "deleted": [],
@@ skipping 16293 matching lines @@
             "path": "touch-events/touch-retargeting.html",
             "url": "/touch-events/touch-retargeting.html"
           }
         ],
         "touch-events/touch-touchevent-constructor.html": [
           {
             "path": "touch-events/touch-touchevent-constructor.html",
             "url": "/touch-events/touch-touchevent-constructor.html"
           }
         ],
+        "uievents/constructors/inputevent-constructor.html": [
+          {
+            "path": "uievents/constructors/inputevent-constructor.html",
+            "url": "/uievents/constructors/inputevent-constructor.html"
+          }
+        ],
         "uievents/legacy-domevents-tests/approved/ProcessingInstruction.DOMCharacterDataModified.html": [
           {
             "path": "uievents/legacy-domevents-tests/approved/ProcessingInstruction.DOMCharacterDataModified.html",
             "url": "/uievents/legacy-domevents-tests/approved/ProcessingInstruction.DOMCharacterDataModified.html"
           }
         ],
         "uievents/legacy-domevents-tests/approved/dispatchEvent.click.checkbox.html": [
           {
             "path": "uievents/legacy-domevents-tests/approved/dispatchEvent.click.checkbox.html",
             "url": "/uievents/legacy-domevents-tests/approved/dispatchEvent.click.checkbox.html"
@@ skipping 4526 matching lines @@
           "url": "/svg/linking/reftests/href-use-element.html"
         }
       ]
     }
   },
   "reftest_nodes": {},
   "rev": null,
   "url_base": "/",
   "version": 3
 }