[Chromedriver] Chromedriver should handle unexpected alert automatically.

chrome/test/chromedriver/session_commands.cc

Index: chrome/test/chromedriver/session_commands.cc
diff --git a/chrome/test/chromedriver/session_commands.cc b/chrome/test/chromedriver/session_commands.cc
index 64d9e97dc7f79c78889ab6fae712a056951e9a77..7601e0122c8f702053fcc32364a0103032c6b8ae 100644
--- a/chrome/test/chromedriver/session_commands.cc
+++ b/chrome/test/chromedriver/session_commands.cc
@@ -128,6 +128,10 @@ std::unique_ptr<base::DictionaryValue> CreateCapabilities(Chrome* chrome) {
   caps->SetBoolean("nativeEvents", true);
   caps->SetBoolean("hasTouchScreen", chrome->HasTouchScreen());
 
+  Session* session = GetThreadLocalSession();
+  caps->SetString("unexpectedAlertBehaviour",
+                   session->GetUnexpectedAlertBehaviour());
+
   ChromeDesktopImpl* desktop = NULL;
   Status status = chrome->GetAsDesktop(&desktop);
   if (status.IsOk()) {
@@ -187,6 +191,9 @@ Status InitSessionHelper(const InitSessionParams& bound_params,
   if (status.IsError())
     return status;
 
+  desired_caps->GetString("unexpectedAlertBehaviour",
+                           &session->unexpected_alert_behaviour);
+
   Log::Level driver_level = Log::kWarning;
   if (capabilities.logging_prefs.count(WebDriverLog::kDriverType))
     driver_level = capabilities.logging_prefs[WebDriverLog::kDriverType];