[Chromedriver] Chromedriver should handle unexpected alert automatically.

chrome/test/chromedriver/client/chromedriver.py

Index: chrome/test/chromedriver/client/chromedriver.py
diff --git a/chrome/test/chromedriver/client/chromedriver.py b/chrome/test/chromedriver/client/chromedriver.py
index 7c075f009caa5b50a0693efce275bd5fd960a8ec..b90a59a75a84f5cb919a7cf62e9a321774e6bf67 100644
--- a/chrome/test/chromedriver/client/chromedriver.py
+++ b/chrome/test/chromedriver/client/chromedriver.py
@@ -111,7 +111,7 @@ class ChromeDriver(object):
                mobile_emulation=None, experimental_options=None,
                download_dir=None, network_connection=None,
                send_w3c_capability=None, send_w3c_request=None,
-               page_load_strategy=None):
+               page_load_strategy=None, unexpected_alert_behaviour=None):
     self._executor = command_executor.CommandExecutor(server_url)
 
     options = {}
@@ -190,6 +190,11 @@ class ChromeDriver(object):
       assert type(page_load_strategy) is str
       params['desiredCapabilities']['pageLoadStrategy'] = page_load_strategy
 
+    if unexpected_alert_behaviour:
+      assert type(unexpected_alert_behaviour) is str
+      params['desiredCapabilities']['unexpectedAlertBehaviour'] = (
+          unexpected_alert_behaviour)
+
     if network_connection:
       params['desiredCapabilities']['networkConnectionEnabled'] = (
           network_connection)