[chromedriver] Implement commands: findChildElement, findChildElements.

chrome/test/chromedriver/js/call_function.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Enum for WebDriver status codes.
  * @enum {number}
  */
 var StatusCode = {
   STALE_ELEMENT_REFERENCE: 10,
@@ skipping 32 matching lines @@
    * Stores a given item in the cache and returns a unique ID.
    *
    * @param {!Object} item The item to store in the cache.
    * @return {number} The ID for the cached item.
    */
   storeItem_: function(item) {
     for (var i in this.cache_) {
       if (item == this.cache_[i])
         return i;
     }
-    this.cache_[this.nextId_] = item;
-    return this.nextId_++;
+    var id = this.nextId_.toString();
+    this.cache_[id] = item;
+    this.nextId_++;
+    return id;
   },
 
   /**
    * Retrieves the cached object for the given ID.
    *
    * @param {number} id The ID for the cached item to retrieve.
    * @return {!Object} The retrieved item.
    */
   retrieveItem_: function(id) {
     var item = this.cache_[id];
@@ skipping 108 matching lines @@
     var returnValue = cache.wrap(func.apply(null, cache.unwrap(args)));
   } catch (error) {
     status = error.code || StatusCode.UNKNOWN_ERROR;
     var returnValue = error.message;
   }
   return {
       status: status,
       value: returnValue
   }
 }