Remove stray underscore in referringVisitId field description.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 2410 matching lines @@
         }
       },
       {
         "id": "VisitItem",
         "type": "object",
         "description": "An object encapsulating one visit to a URL.",
         "properties": {
           "id": {"type": "string", "minimum": 0, "description": "The unique identifier for the item."},
           "visitId": {"type": "string", "description": "The unique identifier for this visit."},
           "visitTime": {"type": "number", "optional": true, "description": "When this visit occurred, represented in milliseconds since the epoch."},
-          "referringVisitId": {"type": "string", "description": "The visit_id of the referrer."},
+          "referringVisitId": {"type": "string", "description": "The visit ID of the referrer."},
           "transition": {
             "type": "string",
             "enum": ["link", "typed", "auto_bookmark", "auto_subframe", "manual_subframe", "generated", "start_page", "form_submit", "reload", "keyword", "keyword_generated"],
             "description": "The <a href='#transition_types'>transition type</a> for this visit from its referrer."
           }
         }
       }
     ],
     "functions": [
       {
@@ skipping 4983 matching lines @@
                 "description": "A string result code. The value is non-empty on success only in tests.",
                 "optional": "true"
               }
             ]
           }
         ]
       }
     ]
   }
 ]