Fix a typo....

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 138 matching lines @@
         ],
         "returns": {
           "type": "array",
           "description": "Array of global objects",
           "items": { "type": "object", "isInstanceOf": "DOMWindow", "properties": {}, "additionalProperties": { "type": "any" } }
         }
       },
       {
         "name": "getBackgroundPage",
         "type": "function",
-        "description": "Returns the JavaScript 'window' object for the background page running inside the current extension. Returns null if the extension has no backround page.",
+        "description": "Returns the JavaScript 'window' object for the background page running inside the current extension. Returns null if the extension has no background page.",
         "parameters": [],
         "returns": {
           "type": "object", "isInstanceOf": "DOMWindow", "properties": {}, "additionalProperties": { "type": "any" }
          }
       },
       {
         "name": "getToolstrips",
         "nodoc": true,
         "type": "function",
         "description": "Deprecated. Please use getViews({type: 'TOOLSTRIP'}). Returns an array of the JavaScript 'window' objects for each of the toolstrip views running inside the current extension. If windowId is specified, returns only the 'window' objects of toolstrips attached to the specified window.",
@@ skipping 4297 matching lines @@
                   "token": { "type": "string", "optional": true }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]