[chromedriver] Implement commands: findChildElement, findChildElements.

chrome/test/chromedriver/webelement.py

+# Copyright (c) 2013 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.
+
+class WebElement(object):
+  """Represents an HTML element."""
+  def __init__(self, chromedriver, id_):
+    self._chromedriver = chromedriver
+    self._id = id_
+
+  def _Execute(self, command, params=None):
+    if params is None:
+      params = {}
+    params['id'] = self._id;
+    return self._chromedriver.ExecuteSessionCommand(command, params)
+
+  def FindElement(self, strategy, target):
+    return self._Execute(
+        'findChildElement', {'using': strategy, 'value': target})
+
+  def FindElements(self, strategy, target):
+    return self._Execute(
+        'findChildElements', {'using': strategy, 'value': target})