[chromedriver] Implement commands: findChildElement, findChildElements.

chrome/test/chromedriver/run_py_tests.py

Index: chrome/test/chromedriver/run_py_tests.py
diff --git a/chrome/test/chromedriver/run_py_tests.py b/chrome/test/chromedriver/run_py_tests.py
index 0df59689fa284b6100b9bd89a394cb5600756440..8bbfc0cd4f4c4cb6e4cb83325e6e847784abad1c 100755
--- a/chrome/test/chromedriver/run_py_tests.py
+++ b/chrome/test/chromedriver/run_py_tests.py
@@ -98,6 +98,24 @@ class ChromeDriverTest(unittest.TestCase):
         'document.body.innerHTML = "<div>a</div><div>b</div>";')
     self.assertEqual(2, len(self._driver.FindElements('tag name', 'div')))
 
+  def testFindChildElement(self):
+    self._driver.ExecuteScript(
+        'document.body.innerHTML = "<div><br><br></div><div><a></a></div>";')
+    element = self._driver.FindElement('tag name', 'div')
+    self.assertEqual(1, len(element))
+    root_id = element['ELEMENT']
+    self.assertEqual(
+        1, len(self._driver.FindChildElement(root_id, 'tag name', 'br')))
+
+  def testFindChildElements(self):
+    self._driver.ExecuteScript(
+        'document.body.innerHTML = "<div><br><br></div><div><br></div>";')
+    element = self._driver.FindElement('tag name', 'div')
+    self.assertEqual(1, len(element))
+    root_id = element['ELEMENT']
+    self.assertEqual(
+        2, len(self._driver.FindChildElements(root_id, 'tag name', 'br')))
+
 
 if __name__ == '__main__':
   parser = optparse.OptionParser()