Only allow extension pages to be displayed in the sidebar to be consistent...

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 3890 matching lines @@
                 "optional": true,
                 "description": "Defaults to the selected tab of the <a href='windows.html#current-window'>current window</a>."
               }
             }
           }
         ]
       },
       {
         "name": "navigate",
         "type": "function",
-        "description": "Navigates sidebar for the specified tab to the specified URL.",
+        "description": "Loads the the specified html file into the sidebar for the specified tab.",
         "parameters": [
           {
             "type": "object",
             "name": "details",
             "properties": {
               "tabId": {
                 "type": "integer",
                 "minimum": 0,
                 "optional": true,
                 "description": "Defaults to the selected tab of the <a href='windows.html#current-window'>current window</a>."
               },
-              "url": { "type": "string" }
+              "path": {
+                "type": "string",
+                "description": "Relative path to the html file in the extension to show in the sidebar."
+              }
             }
           }
         ]
       },
       {
         "name": "getState",
         "type": "function",
         "description": "Returns current sidebar state for the specified tab.",
         "parameters": [
           {
@@ skipping 566 matching lines @@
                   "token": { "type": "string", "optional": true }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]