Add chrome.extension to extension_api.json and docs

chrome/common/extensions/docs/js/api_page_generator.js

 /**
  * @fileoverview This file is the controller for generating extension
  * doc pages.
  *
  * It expects to have available via XHR (relative path):
  *   1) API_TEMPLATE which is the main template for the api pages.
  *   2) A file located at SCHEMA which is shared with the extension system and
  *      defines the methods and events contained in one api.
  *   3) (Possibly) A static version of the current page url in /static/. I.e.
  *      if called as ../foo.html, it will look for ../static/foo.html.
@@ skipping 101 matching lines @@
     else
       console.error("XHR Failed fetching: " + localUrl + "..." + error);
   }
 
   try {
     xhr.onreadystatechange = function(){
       if (xhr.readyState == 4) {
         if (xhr.responseText) {
           window.clearTimeout(abortTimerId);
           onSuccess(xhr.responseText);
-        } else {
-          handleError("responseText empty.");
         }
       }
     }
 
     xhr.onerror = handleError;
 
     xhr.open("GET", url, true);
     xhr.send(null);
   } catch(e) {
     console.log("ex: " + e);
@@ skipping 185 matching lines @@
  * whose |parameters| are json schemas.
  */
 function generateSignatureString(parameters) {
   var retval = [];
   parameters.each(function(param, i) {
     retval.push(param.typeName + " " + param.name);
   });
 
   return retval.join(", ");     
 }