[Chromedriver] Chromedriver should handle unexpected alert automatically.

chrome/test/chromedriver/chrome/chrome_impl.h

Index: chrome/test/chromedriver/chrome/chrome_impl.h
diff --git a/chrome/test/chromedriver/chrome/chrome_impl.h b/chrome/test/chromedriver/chrome/chrome_impl.h
index 17efffd09b7e5b059cac179ff5c4dc896510280b..31bd2f9b9a55f0b546735b6e083756a8022d0f28 100644
--- a/chrome/test/chromedriver/chrome/chrome_impl.h
+++ b/chrome/test/chromedriver/chrome/chrome_impl.h
@@ -43,6 +43,7 @@ class ChromeImpl : public Chrome {
   bool IsMobileEmulationEnabled() const override;
   bool HasTouchScreen() const override;
   std::string page_load_strategy() const override;
+  std::string UnexpectedAlertBehaviour() const override;
   Status Quit() override;
 
  protected:
@@ -50,6 +51,7 @@ class ChromeImpl : public Chrome {
              std::unique_ptr<DevToolsClient> websocket_client,
              ScopedVector<DevToolsEventListener>& devtools_event_listeners,
              std::unique_ptr<PortReservation> port_reservation,
+             std::string unexpected_alert_behaviour,
              std::string page_load_strategy);
 
   virtual Status QuitImpl() = 0;
@@ -67,6 +69,7 @@ class ChromeImpl : public Chrome {
   WebViewList web_views_;
   ScopedVector<DevToolsEventListener> devtools_event_listeners_;
   std::unique_ptr<PortReservation> port_reservation_;
+  std::string unexpected_alert_behaviour_;
   std::string page_load_strategy_;
 };